Epicutaneous Patch Testing Wiki

Hives are a common allergic symptom.

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little problem in most people. 1 These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. 2 Symptoms may include red eyes, an itchy rash, runny nose, shortness of breath, or swelling. 3 Food intolerances and food poisoning are separate conditions. 4 5

Common allergens include pollen and food. Metals and other substances may also cause problems. 1 Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. 6 The underlying mechanism involves immunoglobulin E antibodies IgE, part of the body s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. 7 Diagnosis is typically based on a person s medical history. Further testing of the skin or blood may be useful in certain cases. 5 Positive tests, however, may not mean there is a significant allergy to the substance in question. 8

Early exposure to potential allergens may be protective. 9 Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines. 10 In severe reactions injectable adrenaline epinephrine is recommended. 11 Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear. 10

Allergies are common. 12 In the developed world, about 20 of people are affected by allergic rhinitis, 13 about 6 of people have at least one food allergy, 5 9 and about 20 have atopic dermatitis at some point in time. 14 Depending on the country about 1 and 18 of people have asthma. 15 Anaphylaxis occurs in between 0.05–2 of people. 16 Rates of many allergic diseases appear to be increasing. 11 17 The word allergy was first used by Clemens von Pirquet in 1906. 6

Contents

1 Signs and symptoms

2 Cause

2.1 Foods

2.2 Non-food proteins

2.3 Medications

2.4 Toxins interacting with proteins

2.5 Genetics

2.6 Hygiene hypothesis

2.7 Stress

2.8 Other environmental factors

3 Pathophysiology

3.1 Acute response

3.2 Late-phase response

3.3 Allergic contact dermatitis

4 Diagnosis

4.1 Skin prick testing

4.2 Patch testing

4.3 Blood testing

4.4 Other

4.5 Differential diagnosis

5 Prevention

6 Management

6.1 Medication

6.2 Immunotherapy

6.3 Alternative medicine

7 Epidemiology

7.1 Changing frequency

8 History

8.1 Diagnosis

9 Medical specialty

10 Research

11 See also

12 References

13 External links

Signs and symptoms edit

Common symptoms

Affected organ

Symptom

Nose

swelling of the nasal mucosa allergic rhinitis runny nose, sneezing

Sinuses

allergic sinusitis

Eyes

redness and itching of the conjunctiva allergic conjunctivitis, watery

Airways

Sneezing, coughing, bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as laryngeal edema

Ears

feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.

Skin

rashes, such as eczema and hives urticaria

Gastrointestinal tract

abdominal pain, bloating, vomiting, diarrhea

Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. 18 Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing. 19

Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications like aspirin and antibiotics such as penicillin. Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory asthmatic reactions, or rhinitis. 20 Insect stings, antibiotics, and certain medicines produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system. 21 22 23 Depending on the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma, and even death. This type of reaction can be triggered suddenly, or the onset can be delayed. The severity of this type of allergic response often requires injections of epinephrine, sometimes through a device known as the EpiPen or Twinject auto-injector. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a prolonged period of time. 23

Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema. 24 Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a wheal and flare reaction characteristic of hives and angioedema. 25

Cause edit

Risk factors for allergy can be placed in two general categories, namely host and environmental factors. 26 Host factors include heredity, sex, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes. 27

Foods edit

Main article: Food allergy

A wide variety of foods can cause allergic reactions, but 90 of allergic responses to foods are caused by cow s milk, soy, eggs, wheat, peanuts, tree nuts, fish, and shellfish. 28 Other food allergies, affecting less than 1 person per 10,000 population, may be considered rare. 29

The most common food allergy in the US population is a sensitivity to crustacea. 29 Although peanut allergies are notorious for their severity, peanut allergies are not the most common food allergy in adults or children. Severe or life-threatening reactions may be triggered by other allergens, and are more common when combined with asthma. 28

Rates of allergies differ between adults and children. Peanut allergies can sometimes be outgrown by children. Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5. 30 The sensitivity is usually to proteins in the white, rather than the yolk. 31

Milk-protein allergies are most common in children. 32 Approximately 60 of milk-protein reactions are immunoglobulin E-mediated, with the remaining usually attributable to inflammation of the colon. 33 Some people are unable to tolerate milk from goats or sheep as well as from cows, and many are also unable to tolerate dairy products such as cheese. Roughly 10 of children with a milk allergy will have a reaction to beef. Beef contains a small amount of protein that is present in cow s milk. 34 Lactose intolerance, a common reaction to milk, is not a form of allergy at all, but rather due to the absence of an enzyme in the digestive tract.

Those with tree nut allergies may be allergic to one or to many tree nuts, including pecans, pistachios, pine nuts, and walnuts. 31 Also seeds, including sesame seeds and poppy seeds, contain oils in which protein is present, which may elicit an allergic reaction. 31

Allergens can be transferred from one food to another through genetic engineering; however genetic modification can also remove allergens. Little research has been done on the natural variation of allergen concentrations in the unmodified crops. 35 36

Non-food proteins edit

Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, 1 in 800 surgical patients 0.125 percent reported latex sensitivity, although the sensitivity among healthcare workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of healthcare workers to areas with significant airborne latex allergens, such as operating rooms, intensive-care units, and dental suites. These latex-rich environments may sensitize healthcare workers who regularly inhale allergenic proteins. 37

The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction usually lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations. 37 Anaphylactic reactions occur most often in sensitive patients who have been exposed to a surgeon s latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions. 37

Latex and banana sensitivity may cross-react. Furthermore, those with latex allergy may also have sensitivities to avocado, kiwifruit, and chestnut. 38 These people often have perioral itching and local urticaria. Only occasionally have these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut occurs because latex proteins are structurally homologous with some other plant proteins. 37

Medications edit

About 10 of people report that they are allergic to penicillin; however, 90 turn out not to be. 39 Serious allergies only occur in about 0.03. 39

Toxins interacting with proteins edit

Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak, or poison sumac. Urushiol, which is not itself a protein, acts as a hapten and chemically reacts with, binds to, and changes the shape of integral membrane proteins on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a T-cell-mediated immune response. 40 Of these poisonous plants, sumac is the most virulent. 41 The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking. 42

Estimates vary on the percentage of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to. 0050 milligrams 7.7 10 5 gr of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction. 43

Genetics edit

Allergic diseases are strongly familial: identical twins are likely to have the same allergic diseases about 70 of the time; the same allergy occurs about 40 of the time in non-identical twins. 44 Allergic parents are more likely to have allergic children, 45 and those children s allergies are likely to be more severe than those in children of non-allergic parents. Some allergies, however, are not consistent along genealogies; parents who are allergic to peanuts may have children who are allergic to ragweed. It seems that the likelihood of developing allergies is inherited and related to an irregularity in the immune system, but the specific allergen is not. 45

The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk. 46 Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. 46 The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10. 47

Overall, boys have a higher risk of developing allergies than girls, 45 although for some diseases, namely asthma in young adults, females are more likely to be affected. 48 These differences between the sexes tend to decrease in adulthood. 45

Ethnicity may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to migration. 45 It has been suggested that different genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins. 49

Hygiene hypothesis edit

Main article: Hygiene hypothesis

Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response. Many bacteria and viruses elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease. 50 In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when they are not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects like pollen will trigger an immune response. 51

The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one child. The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that have been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. 52 Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner. 53 The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. 54 The use of antibacterial cleaning products has also been associated with higher incidence of asthma, as has birth by Caesarean section rather than vaginal birth. 55 56

Stress edit

Chronic stress can aggravate allergic conditions. This has been attributed to a T helper 2 TH2 -predominant response driven by suppression of interleukin 12 by both the autonomic nervous system and the hypothalamic–pituitary–adrenal axis. Stress management in highly susceptible individuals may improve symptoms. 57

Other environmental factors edit

International differences have been associated with the number of individuals within a population have allergy. Allergic diseases are more common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations, although these differences are becoming less defined. 58

Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy. 27 Endotoxin exposure reduces release of inflammatory cytokines such as TNF-α, IFNγ, interleukin-10, and interleukin-12 from white blood cells leukocytes that circulate in the blood. 59 Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes. 60

Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies. 61 Recent research has shown that some common parasites, such as intestinal worms e.g., hookworms, secrete chemicals into the gut wall and, hence, the bloodstream that suppress the immune system and prevent the body from attacking the parasite. 62 This gives rise to a new slant on the hygiene hypothesis theory that co-evolution of man and parasites has led to an immune system that functions correctly only in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive. 63 In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants. 64 However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms. 58 Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies. 65 It may be that the term parasite could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work. 65 For more information on this topic, see Helminthic therapy.

Pathophysiology edit

A summary diagram that explains how allergy develops.

Tissues affected in allergic inflammation

Acute response edit

Degranulation process in allergy. Second exposure to allergen. 1 – antigen; 2 – IgE antibody; 3 – FcεRI receptor; 4 – preformed mediators histamine, proteases, chemokines, heparin ; 5 – granules; 6 – mast cell; 7 – newly formed mediators prostaglandins, leukotrienes, thromboxanes, PAF

In the early stages of allergy, a type I hypersensitivity reaction against an allergen encountered for the first time and presented by a professional antigen-presenting cell causes a response in a type of immune cell called a TH2 lymphocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 IL-4. These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a particular type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor a kind of Fc receptor called FcεRI on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen. 27

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators cytokines, interleukins, leukotrienes, and prostaglandins from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide classical anaphylaxis, or localized to particular body systems; asthma is localized to the respiratory system and eczema is localized to the dermis. 27

Late-phase response edit

After the chemical mediators of the acute response subside, late-phase responses can often occur. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site. The reaction is usually seen 2–24 hours after the original reaction. 66 Cytokines from mast cells may play a role in the persistence of long-term effects. Late-phase responses seen in asthma are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils and are still dependent on activity of TH2 cells. 67

Allergic contact dermatitis edit

Although allergic contact dermatitis is termed an allergic reaction which usually refers to type I hypersensitivity, its pathophysiology actually involves a reaction that more correctly corresponds to a type IV hypersensitivity reaction. 68 In type IV hypersensitivity, there is activation of certain types of T cells CD8 that destroy target cells on contact, as well as activated macrophages that produce hydrolytic enzymes.

Diagnosis edit

An allergy testing machine being operated in the diagnostic immunology lab

Effective management of allergic diseases relies on the ability to make an accurate diagnosis. 69 Allergy testing can help confirm or rule out allergies. 70 71 Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life. 70 To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy blood test. Both methods are recommended, and they have similar diagnostic value. 71 72

Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test. 70 Also, early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions. 73

Allergy undergoes dynamic changes over time. Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life. Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat have been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish. 71 Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet. 74

Skin prick testing edit

Skin testing on arm

Skin testing on back

Skin testing is also known as puncture testing and prick testing due to the series of tiny punctures or pricks made into the patient s skin. Small amounts of suspected allergens and/or their extracts e.g., pollen, grass, mite proteins, peanut extract are introduced to sites on the skin marked with pen or dye the ink/dye should be carefully selected, lest it cause an allergic response itself. A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected intradermally into the patient s skin, with a needle and syringe. Common areas for testing include the inside forearm and the back.

If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to a full-blown hive called wheal and flare in more sensitive patients similar to a mosquito bite. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with /- meaning borderline reactivity, and 4 being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature. 75 Some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy. 76

If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease, or has taken antihistamines in the last several days.

Patch testing edit

Patch test

Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed reactions. It is used to help ascertain the cause of skin contact allergy, or contact dermatitis. Adhesive patches, usually treated with a number of common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, usually at 48 hours after application of the patch, and again two or three days later.

Blood testing edit

An allergy blood test is quick and simple, and can be ordered by a licensed health care provider e.g., an allergy specialist, GP, or PED. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can take an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin tests.

An allergy blood test is available through most laboratories. A sample of the patient s blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the person is not exposed to any allergens during the testing procedure.

The test measures the concentration of specific IgE antibodies in the blood. Quantitative IgE test results increase the possibility of ranking how different substances may affect symptoms. A rule of thumb is that the higher the IgE antibody value, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can nevertheless help predict future symptom development. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity. 77 78

A low total IgE level is not adequate to rule out sensitization to commonly inhaled allergens. 79 Statistical methods, such as ROC curves, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.

Other edit

Challenge testing: Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes. Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an allergist.

Elimination/Challenge tests: This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be challenged by reintroducing the allergen, to see if symptoms are reproduced.

Unreliable tests: There are other types of allergy testing methods that are unreliable, including applied kinesiology allergy testing through muscle relaxation, cytotoxicity testing, urine autoinjection, skin titration Rinkel method, and provocative and neutralization subcutaneous testing or sublingual provocation. 80

Differential diagnosis edit

Before a diagnosis of allergic disease can be confirmed, other possible causes of the presenting symptoms should be considered. 81 Vasomotor rhinitis, for example, is one of many maladies that shares symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis. 82 Once a diagnosis of asthma, rhinitis, anaphylaxis, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.

Prevention edit

The consumption of various foods during pregnancy has been linked to eczema; these include celery, citrus fruit, raw pepper, margarine, and vegetable oil. 83 A high intake of antioxidants, zinc, and selenium during pregnancy may help prevent allergies. This is linked to a reduced risk for childhood-onset asthma, wheezing, and eczema. 84 Further research needs to be conducted. Probiotic supplements taken during pregnancy or infancy may help to prevent atopic dermatitis. 85 After birth, an early introduction of solid food and high diversity before week 17 could increase a child s risk for allergies. Studies suggest that introduction of solid food and avoidance of highly allergenic food such as peanuts during the first year does not help in allergy prevention. 83

Management edit

Management of allergies typically involves avoiding what triggers the allergy and medications to improve the symptoms. 10 Allergen immunotherapy may be useful for some types of allergies. 10

Medication edit

Several medications maybe used to block the action of allergic mediators, or to prevent activation of cells and degranulation processes. These include antihistamines, glucocorticoids, epinephrine, mast cell stabilizers, and antileukotriene agents are common treatments of allergic diseases. 86 Anti-cholinergics, decongestants, and other compounds thought to impair eosinophil chemotaxis, are also commonly used. Epinephrine is important in anaphylaxis.

Immunotherapy edit

Main article: Allergen immunotherapy

Anti-allergy immunotherapy

Allergen immunotherapy is useful for environmental allergies, allergies to insect bites, and asthma. 10 87 Its benefit for food allergies is unclear and thus not recommended. 10 Immunotherapy involves exposing people to larger and larger amounts of allergen in an affect to change the immune system s response. 10

Meta-analyses have found that injections of allergens under the skin is effective in the treatment in allergic rhinitis in children 88 89 and in asthma. 87 The benefits may last for years after treatment is stopped. 90 It is generally safe and effective for allergic rhinitis and conjunctivitis, allergic forms of asthma, and stinging insects. 91

The evidence also supports the use of sublingual immunotherapy for rhinitis and asthma but it is less strong. 90 For seasonal allergies the benefit is small. 92 In this form the allergen is given under the tongue and people often prefer it to injections. 90 Immunotherapy is not recommended as a stand-alone treatment for asthma. 90

Alternative medicine edit

An experimental treatment, enzyme potentiated desensitization EPD, has been tried for decades but is not generally accepted as effective. 93 EPD uses dilutions of allergen and an enzyme, beta-glucuronidase, to which T-regulatory lymphocytes are supposed to respond by favoring desensitization, or down-regulation, rather than sensitization. EPD has also been tried for the treatment of autoimmune diseases but evidence does not show effectiveness. 93

A review found no effectiveness of homeopathic treatments and no difference compared with placebo. The authors concluded that, based on rigorous clinical trials of all types of homeopathy for childhood and adolescence ailments, there is no convincing evidence that supports the use of homeopathic treatments. 94

Epidemiology edit

The allergic diseases hay fever and asthma have increased in the Western world over the past 2–3 decades. 95 Increases in allergic asthma and other atopic disorders in industrialized nations, it is estimated, began in the 1960s and 1970s, with further increases occurring during the 1980s and 1990s, 96 although some suggest that a steady rise in sensitization has been occurring since the 1920s. 97 The number of new cases per year of atopy in developing countries has, in general, remained much lower. 96

Allergic conditions: Statistics and Epidemiology

Allergy type

United States

United Kingdom 98

Allergic rhinitis

35.9 million 99 about 11 of the population 100

3.3 million about 5.5 of the population 101

Asthma

10 million have allergic asthma about 3 of the population. The prevalence of asthma increased 75 from 1980 to 1994. Asthma prevalence is 39 higher in African Americans than in Europeans. 102

5.7 million about 9.4. In six- and seven-year-olds asthma increased from 18.4 to 20.9 over five years, during the same time the rate decreased from 31 to 24.7 in 13- to 14-year-olds.

Atopic eczema

About 9 of the population. Between 1960 and 1990 prevalence has increased from 3 to 10 in children. 103

5.8 million about 1 severe.

Anaphylaxis

At least 40 deaths per year due to insect venom. About 400 deaths due to penicillin anaphylaxis. About 220 cases of anaphylaxis and 3 deaths per year are due to latex allergy. 104 An estimated 150 people die annually from anaphylaxis due to food allergy. 105

Between 1999 and 2006, 48 deaths occurred in people ranging from five months to 85 years old.

Insect venom

Around 15 of adults have mild, localized allergic reactions. Systemic reactions occur in 3 of adults and less than 1 of children. 106

Unknown

Drug allergies

Anaphylactic reactions to penicillin cause 400 deaths per year.

Food allergies

About 6 of US children under age 3 and 3.5–4 of the overall US population. citation needed Peanut and/or tree nut e.g. walnut allergy affects about three million Americans, or 1.1 of the population. 105

5–7 of infants and 1–2 of adults. A 117.3 increase in peanut allergies was observed from 2001 to 2005, an estimated 25,700 people in England are affected.

Multiple allergies Asthma, eczema and allergic rhinitis together

2.3 million about 3.7, prevalence has increased by 48.9 between 2001 and 2005. 107

Changing frequency edit

Although genetic factors govern susceptibility to atopic disease, increases in atopy have occurred within too short a time frame to be explained by a genetic change in the population, thus pointing to environmental or lifestyle changes. 96 Several hypotheses have been identified to explain this increased rate; increased exposure to perennial allergens due to housing changes and increasing time spent indoors, and changes in cleanliness or hygiene that have resulted in the decreased activation of a common immune control mechanism, coupled with dietary changes, obesity and decline in physical exercise. 95 The hygiene hypothesis maintains 108 that high living standards and hygienic conditions exposes children to fewer infections. It is thought that reduced bacterial and viral infections early in life direct the maturing immune system away from TH1 type responses, leading to unrestrained TH2 responses that allow for an increase in allergy. 63 109

Changes in rates and types of infection alone however, have been unable to explain the observed increase in allergic disease, and recent evidence has focused attention on the importance of the gastrointestinal microbial environment. Evidence has shown that exposure to food and fecal-oral pathogens, such as hepatitis A, Toxoplasma gondii, and Helicobacter pylori which also tend to be more prevalent in developing countries, can reduce the overall risk of atopy by more than 60, 110 and an increased rate of parasitic infections has been associated with a decreased prevalence of asthma. 111 It is speculated that these infections exert their effect by critically altering TH1/TH2 regulation. 112 Important elements of newer hygiene hypotheses also include exposure to endotoxins, exposure to pets and growing up on a farm. 112

History edit

The concept of allergy was originally introduced in 1906 by the Viennese pediatrician Clemens von Pirquet, after he noted that some of his patients were hypersensitive to normally innocuous entities such as dust, pollen, or certain foods. 113 Pirquet called this phenomenon allergy from the Ancient Greek words ἄλλος allos meaning other and ἔργον ergon meaning work. 114

All forms of hypersensitivity used to be classified as allergies, and all were thought to be caused by an improper activation of the immune system. Later, it became clear that several different disease mechanisms were implicated, with the common link to a disordered activation of the immune system. In 1963, a new classification scheme was designed by Philip Gell and Robin Coombs that described four types of hypersensitivity reactions, known as Type I to Type IV hypersensitivity. 115 With this new classification, the word allergy was restricted to type I hypersensitivities also called immediate hypersensitivity, which are characterized as rapidly developing reactions.

A major breakthrough in understanding the mechanisms of allergy was the discovery of the antibody class labeled immunoglobulin E IgE – Kimishige Ishizaka and co-workers were the first to isolate and describe IgE in the 1960s. 116

Radiometric assays include the radioallergosorbent test RAST test method, which uses IgE-binding anti-IgE antibodies labeled with radioactive isotopes for quantifying the levels of IgE antibody in the blood. 117 Other newer methods use colorimetric or fluorescence-labeled technology in the place of radioactive isotopes. citation needed

The RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB, Uppsala, Sweden, and the acronym RAST is actually a brand name. In 1989, Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which uses the newer fluorescence-labeled technology. citation needed

American College of Allergy Asthma and Immunology ACAAI and the American Academy of Allergy Asthma and Immunology AAAAI issued the Joint Task Force Report Pearls and pitfalls of allergy diagnostic testing in 2008, and is firm in its statement that the term RAST is now obsolete:

The term RAST became a colloquialism for all varieties of in vitro allergy tests. This is unfortunate because it is well recognized that there are well-performing tests and some that do not perform so well, yet they are all called RASTs, making it difficult to distinguish which is which. For these reasons, it is now recommended that use of RAST as a generic descriptor of these tests be abandoned. 118

The new version, the ImmunoCAP Specific IgE blood test, is the only specific IgE assay to receive FDA approval to quantitatively report to its detection limit of 0.1kU/l. citation needed

Medical specialty edit

An allergist is a physician specially trained to manage and treat allergies, asthma and the other allergic diseases. In the United States physicians holding certification by the American Board of Allergy and Immunology ABAI have successfully completed an accredited educational program and evaluation process, including a proctored examination to demonstrate knowledge, skills, and experience in patient care in allergy and immunology. 119 Becoming an allergist/immunologist requires completion of at least nine years of training. After completing medical school and graduating with a medical degree, a physician will undergo three years of training in internal medicine to become an internist or pediatrics to become a pediatrician. Once physicians have finished training in one of these specialties, they must pass the exam of either the American Board of Pediatrics ABP, the American Osteopathic Board of Pediatrics AOBP, the American Board of Internal Medicine ABIM, or the American Osteopathic Board of Internal Medicine AOBIM. Internists or pediatricians wishing to focus on the sub-specialty of allergy-immunology then complete at least an additional two years of study, called a fellowship, in an allergy/immunology training program. Allergist/immunologists listed as ABAI-certified have successfully passed the certifying examination of the ABAI following their fellowship. 120

In the United Kingdom, allergy is a subspecialty of general medicine or pediatrics. After obtaining postgraduate exams MRCP or MRCPCH, a doctor works for several years as a specialist registrar before qualifying for the General Medical Council specialist register. Allergy services may also be delivered by immunologists. A 2003 Royal College of Physicians report presented a case for improvement of what were felt to be inadequate allergy services in the UK. 121 In 2006, the House of Lords convened a subcommittee. It concluded likewise in 2007 that allergy services were insufficient to deal with what the Lords referred to as an allergy epidemic and its social cost; it made several recommendations. 122

Research edit

Low-allergen foods are being developed, as are improvements in skin prick test predictions; evaluation of the atopy patch test; in wasp sting outcomes predictions and a rapidly disintegrating epinephrine tablet, and anti-IL-5 for eosinophilic diseases. 123

Aerobiology is the study of biological particles passively dispersed through the air. One aim is the prevention of allergies due to pollen. 124 125

See also edit

List of allergens

Oral allergy syndrome

References edit

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Allergy at DMOZ

Basic Pathology - Robbins et al - 9th edition

Retrieved from https://en.wikipedia.org/w/index.php.title Allergy oldid 694066353

Categories: AllergologyEffects of external causesImmunologyRespiratory diseasesImmune system.

epicutaneous patch testing wiki

Skin allergy testing is a method for medical diagnosis of allergies that attempts to provoke a small, controlled, allergic response.

Contents

1 Methods

1.1 Immediate reactions tests

1.2 Delayed reactions tests

1.3 Skin end point titration

2 Preparation

3 Contraindications

4 See also

5 References

6 External links

Methods edit

A microscopic amount of an allergen is introduced to a patient s skin by various means: 1

A person receiving a skin allergy test

Skin prick test: pricking the skin with a needle or pin containing a small amount of the allergen. 2

Skin scratch test: a deep dermic scratch is performed with help of the blunt botton of a lancet. 3

Intradermic test: a tiny quantity of allergen is injected under the dermis wth a hypodermic syringe.

Skin scrape Test: a superficial scrape is performed with help of the bovel of a needle to remove the superficial layer of the epidermis. 4

Patch test: applying a patch to the skin, where the patch contains the allergen

If an immuno-response is seen in the form of a rash, urticaria hives, or worse anaphylaxis it can be concluded that the patient has a hypersensitivity or allergy to that allergen. Further testing can be done to identify the particular allergen.

The skin scratch test as it s called, is not very commonly used due to increased likelihood of infection. On the other hand, the skin scrape test is painless, does not leave residual pigmentation and does not have a risk of infection, since it is limited to the superficial layer of the skin.

Some allergies are identified in a few minutes but others may take several days. In all cases where the test is positive, the skin will become raised, red and appear itchy. The results are recorded - larger wheals indicating that the subject is more sensitive to that particular allergen. A negative test does not conclusively rule out an allergy; occasionally, the concentration needs to be adjusted, or the body fails to elicit a response.

Immediate reactions tests edit

Skin testing on arm

In the prick, scratch and scrape tests, a few drops of the purified allergen are gently pricked on to the skin surface, usually the forearm. This test is usually done in order to identify allergies to pet dander, dust, pollen, foods or dust mites. Intradermal injections are done by injecting a small amount of allergen just beneath the skin surface. The test is done to assess allergies to drugs like penicillin or bee venom.

Skin testing on back

To ensure that the skin is reacting in the way it is supposed to, all skin allergy tests are also performed with proven allergens like histamine or glycerin. The majority of people do react to histamine and do not react to glycerin. If the skin does not react appropriately to these allergens then it most likely will not react to the other allergens. These results are interpreted as falsely negative. 5

Delayed reactions tests edit

See also: Patch test

Patch test

The patch test simply uses a large patch which has different allergens on it. The patch is applied onto the skin, usually on the back. The allergens on the patch include latex, medications, preservatives, hair dyes, fragrances, resins and various metals. When a patch is applied the subject should avoid bathing or exercise for at least 48 hours.

Skin end point titration edit

Also called an intradermal test, this skin end point titration SET uses intradermal injection of allergens at increasing concentrations to measure allergic response. 6 To prevent a severe allergic reaction, the test is started with a very dilute solution. After 10 minutes, the injection site is measured to look for growth of wheal, a small swelling of the skin. Two millimeters of growth in 10 minutes is considered positive. If 2 mm of growth is noted, then a second injection at a higher concentration is given to confirm the response. The end point is the concentration of antigen that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal grows larger than 13 mm, then no further injection are given since this is considered a major reaction.

Preparation edit

There are no major preparations required for skin testing. At the first consult, the subject s medical history is obtained and physical examination is performed. All consumers should bring a list of their medications because some may interfere with the testing. Other medications may increase the chance of a severe allergic reaction. Medications that commonly interfere with skin testing include the following:

Histamine antagonists like Allegra, Claritin, Benadryl, Zyrtec

Antidepressants like Amitriptyline, Doxepin

Antacid like Tagamet or Zantac

Consumers who undergo skin testing should know that anaphylaxis can occur anytime. So if any of the following symptoms are experienced, a physician consultation is recommended immediately:

Low grade Fever

Lightheadedness or dizziness

Wheezing or Shortness of breath

Extensive skin rash

Swelling of face, lips or mouth

Difficulty swallowing or speaking

Contraindications edit

Even though skin testing may seem to be a benign procedure, it does have some risks, including swollen red bumps hives which may occur after the test. The hives usually disappear in a few hours after the test. In rare cases they can persist for a day or two. These hives may be itchy and are best treated by applying an over the counter hydrocortisone cream. 7 In very rare cases one may develop a full blown allergic reaction. Physicians who perform skin test always have equipment and medications available in case an anaphylaxis reaction occurs. This is the main reason why consumers should not get skin testing performed at corner stores or by people who have no medical training. 8

Skin testing can be done on individuals of all ages. However, there are times when a skin test should not be done. Individuals who take medications for depression, gastric acidity or antihistamines should not undergo this test. In such cases, stopping the medications for a skin test may not be worthwhile as one may develop symptoms from the untreated medical disorders. Individuals who have severe, generalized skin disease or an acute skin infection should not undergo skin testing. One needs uninvolved skin for testing.

There are some individuals who are highly sensitive to even the smallest amount of allergen and in such scenarios, allergic testing is not recommended. Whenever the chances of an anaphylactic shock are high, the test is best avoided. 9

Besides skin tests, there are blood tests which measure a specific antibody in the blood. The IgE antibody plays a vital role in allergies but its levels in blood do not always correlate with the allergic reaction. 10

There are many alternative health care practitioners who perform a variety of provocation neutralization tests, but the vast majority of these tests have no validity and have never been proven to work scientifically.

See also edit

RAST test

Basophil activation

Allergies

Hypersensitivity

Dermatitis

Anaphylaxis

Prausnitz-Küstner test

List of allergies

References edit

Bernstein IL, Li JT, Bernstein DI, Hamilton R, Spector SL, Tan R, et al. Allergy diagnostic testing: an updated practice parameter. Ann Allergy Asthma Immunol 2008; 100:S1-148.

Basomba A, Sastre A, Pelaez A, Romar A, Campos A, Garcia-Villalmanzo A. Standardization of the prick test. A comparative study of three methods. Allergy 1985; 5-9.

Indrajana T, Spieksma FT, Voorhorst R. Comparative study of the intracutaneous, scratch and prick tests in allergy. Ann Allergy 1971; 9-50.

Olivier CE, Argentão DGP, Santos RAPG, Silva MD, Lima RPS, Zollner RL. Skin scrape test: an inexpensive and painless skin test for recognition of immediate hypersensitivity in children and adults. The Open Allergy Journal 2013; 6:9-17. Link

American Academy of Allergy Asthma Immunology: What is Allergy Testing., Retrieved on 2010-01-20.

Skin Test End-Point Titration at the US National Library of Medicine Medical Subject Headings MeSH

Skin Testing and Allergy Injection Treatment for Allergies and Asthma - The University of Arizona Health Sciences Center, Retrieved on 2010-01-20.

Allergy Testing - August 15,2002 - American Family Physician, Retrieved on 2010-01-20.

Skin test for Allergy, Retrieved on 2010-01-20.

Skin Testing Basic Information, Retrieved on 2010-01-20.

External links edit

Wikimedia Commons has media related to Skin allergy test.

The British Institute for Allergies

About.com - allergy tests

Skin Patches Allergy Testing

Retrieved from https://en.wikipedia.org/w/index.php.title Skin_allergy_test oldid 667465682

Categories: AllergologySkin testsDermatologic proceduresImmunologic tests.

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