What does h mean in allergy test

Even though skin testing may seem to be a benign procedure, it does own some risks, including swollen red bumps (hives) which may happen after the test. The hives generally vanish 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.[8] In extremely rare cases one may develop a full blown allergic reaction. Physicians who act out skin test always own 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 own no medical training.

Antihistamines, which are commonly used to treat allergy symptoms, interfere with skin tests, as they can prevent the skin from reacting to the allergens being tested. People who take an antihistamine need either to select a diverse form of allergy test or to stop taking the antihistimine temporarily before the test. The period of time needed can range from a day or two to 10 days or longer, depending on the specific medication. Some medications not primarily used as antihistamines, including tricyclic antidepressants, phenothiazine-based antipsychotics, and several kinds of medications used for gastrointestinal disorders, can similarly interfere with skin tests.[9]

People who own severe, generalized skin disease or an acute skin infection should not undergo skin testing, as one needs uninvolved skin for testing.

Also, skin testing should be avoided for people at a heightened risk of anaphylactic shock, including people who are known to be highly sensitive to even the smallest quantity of allergen.[10]

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.[11]

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


Signs and symptoms

Affected organ Common signs and symptoms
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.[21] Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.[22]

Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications love 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.[23] Insect stings, food, antibiotics, and certain medicines may 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.[24][25][26] Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death.

This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.[26]

Skin

Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema.[27] Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a «weal and flare» reaction characteristic of hives and angioedema.[28]

With insect stings a large local reaction may happen (an area of skin redness greater than 10 cm in size).[29] It can final one to two days.[29] This reaction may also happen after immunotherapy.[30]


Preparation

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. Every 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:

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

  1. Swelling of face, lips or mouth
  2. Lightheadedness or dizziness
  3. Wheezing or Shortness of breath
  4. Low grade Fever
  5. Extensive skin rash
  6. Difficulty swallowing or speaking


Methods

A microscopic quantity of an allergen is introduced to a patient’s skin by various means:[1]

  1. Skin scrape Test: a superficial scrape is performed with assist of the bovel of a needle to remove the superficial layer of the epidermis.[4]
  2. Skin scratch test: a deep dermic scratch is performed with assist of the blunt bottom of a lancet.[3]
  3. Skin prick test: pricking the skin with a needle or pin containing a little quantity of the allergen.[2]
  4. Intradermic test: a tiny quantity of allergen is injected under the dermis with a hypodermic syringe.
  5. 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 specific allergen.

The «skin scratch test» as it is called, is not extremely 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 own 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 every 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 specific allergen. A negative test does not conclusively law out an allergy; occasionally, the concentration needs to be adjusted, or the body fails to elicit a response.

Delayed reactions tests

See also: Patch test

The patch test simply uses a large patch which has diverse allergens on it.

The patch is applied onto the skin, generally on the back. The allergens on the patch include latex, medications, preservatives, hair dyes, fragrances, resins and various metals.

Immediate reactions tests

In the prick, scratch and scrape tests, a few drops of the purified allergen are gently pricked on to the skin surface, generally the forearm. This test is generally done in order to identify allergies to pet dander, dust, pollen, foods or dust mites. Intradermal injections are done by injecting a little quantity of allergen just beneath the skin surface. The test is done to assess allergies to drugs love penicillin[5] or bee venom.

To ensure that the skin is reacting in the way it is supposed to, every skin allergy tests are also performed with proven allergens love histamine, and non-allergens love 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.[6]

Skin finish point titration

Also called an intradermal test, this skin finish point titration (SET) uses intradermal injection of allergens at increasing concentrations to measure allergic response.[7] To prevent a severe allergic reaction, the test is started with a extremely dilute solution.

After 10 minutes, the injection site is measured to glance for growth of wheal, a little swelling of the skin. Two millimeters of growth in 10 minutes is considered positive.

What does h mean in allergy test

If 2 mm of growth is noted, then a second injection at a higher concentration is given to confirm the response. The finish 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.


External links

A person receiving a skin allergy test

  • ^Skin test for Allergy, Retrieved on 2010-01-20.
  • ^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. LinkArchived August 3, 2013, at the Wayback Machine

  • ^Marwood, Joseph; Aguirrebarrena, Gonzalo; Kerr, Stephen; Welch, Susan A; Rimmer, Janet (2017-10-01). «De-labelling self-reported penicillin allergy within the emergency department through the use of skin tests and oral drug provocation testing». Emergency Medicine Australasia. 29 (5): 509–515. doi:10.1111/1742-6723.12774. ISSN 1742-6723.

    PMID 28378949.

  • ^Basomba A, Sastre A, Pelaez A, Romar A, Campos A, Garcia-Villalmanzo A. Standardization of the prick test.

    What does h mean in allergy test

    A comparative study of three methods. Allergy 1985; 40:395-9.

  • ^Skin Test End-Point Titration at the US National Library of Medicine Medical Subject Headings (MeSH)
  • ^Indrajana T, Spieksma FT, Voorhorst R. Comparative study of the intracutaneous, scratch and prick tests in allergy. Ann Allergy 1971; 29:639-50.
  • ^Allergy Testing — August 15,2002 — American Family Physician, Retrieved on 2010-01-20.
  • ^American Academy of Allergy Asthma & Immunology: What is Allergy Testing?, Retrieved on 2010-01-20.

    |archive-url=https://web.archive.org/web/20120120175201/https://www.aaaai.org/conditions-and-treatments/library/at-a-glance/allergy-testing.aspx |archive-date=20 January 2012

  • ^Skin Testing and Allergy Injection Treatment for Allergies and Asthma — The University of Arizona Health Sciences Middle, Retrieved on 2010-01-20.
  • ^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.
  • ^Skin Testing Basic Information, Retrieved on 2010-01-20. Archived January 14, 2010, at the Wayback Machine

A limitation of allergy blood tests is that there is no gold-standard test for numerous allergic conditions.

(Double-blind, placebo-controlled oral food challenge testing has been proposed as the gold-standard test for food allergy, and nasal allergen provocation challenge has been proposed for allergic rhinitis.)

Also, allergy blood tests can give false-positive results because of nonspecific binding of antibody in the assay.

Of note: evidence of sensitization to a specific allergen (ie, a positive blood test result) is not synonymous with clinically relevant disease (ie, clinical sensitivity).

Conversely, these tests can give false-negative results in patients who own true IgE-mediated disease as confirmed by skin testing or allergen challenge.

The sensitivity of blood allergy testing is approximately 25% to 30% lower than that of skin testing, based on comparative studies.2 The blood tests are generally considered positive if the allergen-specific IgE level is greater than 0.35 kU/L; however, sensitization to certain inhalant allergens can happen at levels as low as 0.12 kU/L.14

Specific IgE levels measured by diverse commercial assays are not always interchangeable or equivalent, so a clinician should consistently select the same immunoassay if possible when assessing any given patient over time.15

Levels of specific IgE own been shown to depend on age, allergen specificity, entire serum IgE, and, with inhalant allergens, the season of the year.15,16

Other limitations of blood testing are its cost and a delay of several days to a week in obtaining the results.17

The allergy evaluation should start with a thorough history to glance for possible triggers for the patient’s symptoms.

For example, respiratory conditions such as asthma and rhinitis may be exacerbated during specific times of the year when certain pollens are commonly present.

For patients with this pattern, blood testing for allergy to common inhalants, including pollens, may be appropriate.

What does h mean in allergy test

Similarly, peanut allergy evaluation is indicated for a kid who has suffered an anaphylactic reaction after consuming peanut butter. Blood testing is also indicated in patients with a history of venom anaphylaxis, especially if venom skin testing was negative.

In cases in which the patient does not own a clear history of sensitization, blood testing for allergy to multiple foods may discover evidence of sensitization that does not necessarily correlate with clinical disease.18

Likewise, blood tests are not likely to be clinically relevant in conditions not mediated by IgE, such as food intolerances (eg, lactose intolerance), celiac disease, the DRESS syndrome (drug rash, eosinophilia, and systemic symptoms), Stevens-Johnson syndrome, toxic epidermal necrolysis, or other types of drug hypersensitivity reactions, such as serum sickness.3

Tests for allergy to hundreds of substances are available.

Foods

Milk, eggs, soy, wheat, peanuts, tree nuts, fish, and shellfish account for most cases of food allergy in the United States.18

IgE-mediated hypersensitivity to milk, eggs, and peanuts tends to be more common in children, whereas peanuts, tree nuts, fish, and shellfish are more commonly associated with reactions in adults.18 Children are more likely to outgrow allergy to milk, soy, wheat, and eggs than allergy to peanuts, tree nuts, fish, and shellfish—only about 20% of children outgrow peanut allergy.18

Patients with an IgE-mediated reaction to foods should be closely followed by a specialist, who can best assist determine the appropriateness of additional testing (such as an oral challenge under observation), avoidance recommendations, and the introduction of foods back into the diet.19

Specific IgE tests for allergy to a variety of foods are available and can be extremely useful for diagnosis when used in the appropriate setting.

Double-blind, placebo-controlled studies own established a relationship between quantitative levels of specific IgE and the 95% likelihood of experiencing a subsequent clinical reaction upon exposure to that allergen.

What does h mean in allergy test

One of the most frequently cited studies is summarized in Table 1.7,8,18 In numerous of these studies the gold standard for food allergy was a positive double-blind, placebo-controlled oral food challenge. Of note, these values predict the likelihood of a clinical reaction but not necessarily its severity.

One caveat about these studies is that numerous were initially performed in children with a history of food allergy, numerous of whom had atopic dermatitis, and the findings own not been systematically reexamined in larger studies in more heterogeneous populations.

For example, at least eight studies tried to identify a diagnostic IgE level for cow’s milk allergy.

The 95% confidence intervals varied widely, depending on the study design, the age of the study population, the prevalence of food allergy in the population, and the statistical method used for analysis.5 For most other foods for which blood tests are available, few studies own been performed to establish predictive values similar to those in Table 1.

Thus, slight elevations in antigen-specific IgE (> 0.35 kU/L) may correlate only with in vitro sensitization in a patient who has no clinical reactivity upon oral exposure to a specific antigen.

Broad food panels own been shown to own false-positive rates higher than 50%—ie, in more than half of cases, positive results own no clinical relevance.

Therefore, these large food panels should not be used for screening.19 Instead, it is recommended that tests be limited to relevant foods based on the patient’s history when evaluating symptoms consistent with an IgE-mediated reaction to a specific food.

Food-specific IgE evaluation is also not helpful in evaluating non-IgE adverse reactions to foods (eg, intolerances).

Therefore, the patient’s history remains the most significant tool for evaluation of food allergy. In cases in which the patient’s history suggests a food-associated IgE-mediated reaction and the blood test is negative, the patient should be referred to a specialist for skin testing with commercial extracts or even unused food extracts, given the higher sensitivity of in vivo testing.20

Immune system response to a substance that most people tolerate well

For the medical journal of this title, see Allergy (journal).

Allergy
Hives are a common allergic symptom
Specialty Immunology
Symptoms Red eyes, itchy rash, runny nose, shortness of breath, swelling, sneezing[1]
Types Hay fever, food allergies, atopic dermatitis, allergic asthma, anaphylaxis[2]
Causes Genetic and environmental factors[3]
Diagnostic method Based on symptoms, skin prick test, blood test[4]
Differential diagnosis Food intolerances, food poisoning[5]
Prevention Early exposure to potential allergens[6]
Treatment Avoiding known allergens, medications, allergen immunotherapy[7]
Medication Steroids, antihistamines, epinephrine, mast cell stabilizers, antileukotrienes[7][8][9][10]
Frequency Common[11]

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[12] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[2] Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling.[1]Food intolerances and food poisoning are separate conditions.[4][5]

Common allergens include pollen and certain foods.[12] Metals and other substances may also cause problems.[12] Food, insect stings, and medications are common causes of severe reactions.[3] Their development is due to both genetic and environmental factors.[3] 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.[13] Diagnosis is typically based on a person’s medical history.[4] Further testing of the skin or blood may be useful in certain cases.[4] Positive tests, however, may not mean there is a significant allergy to the substance in question.[14]

Early exposure to potential allergens may be protective.[6] Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines.[7] In severe reactions injectable adrenaline (epinephrine) is recommended.[8]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.[7] Its use in food allergies is unclear.[7]

Allergies are common.[11] In the developed world, about 20% of people are affected by allergic rhinitis,[15] about 6% of people own at least one food allergy,[4][6] and about 20% own atopic dermatitis at some point in time.[16] Depending on the country about 1–18% of people own asthma.[17][18] Anaphylaxis occurs in between 0.05–2% of people.[19] Rates of numerous allergic diseases appear to be increasing.[8][20] The expression «allergy» was first used by Clemens von Pirquet in 1906.[3]

A limitation of allergy blood tests is that there is no gold-standard test for numerous allergic conditions.

What does h mean in allergy test

(Double-blind, placebo-controlled oral food challenge testing has been proposed as the gold-standard test for food allergy, and nasal allergen provocation challenge has been proposed for allergic rhinitis.)

Also, allergy blood tests can give false-positive results because of nonspecific binding of antibody in the assay.

Of note: evidence of sensitization to a specific allergen (ie, a positive blood test result) is not synonymous with clinically relevant disease (ie, clinical sensitivity).

Conversely, these tests can give false-negative results in patients who own true IgE-mediated disease as confirmed by skin testing or allergen challenge.

The sensitivity of blood allergy testing is approximately 25% to 30% lower than that of skin testing, based on comparative studies.2 The blood tests are generally considered positive if the allergen-specific IgE level is greater than 0.35 kU/L; however, sensitization to certain inhalant allergens can happen at levels as low as 0.12 kU/L.14

Specific IgE levels measured by diverse commercial assays are not always interchangeable or equivalent, so a clinician should consistently select the same immunoassay if possible when assessing any given patient over time.15

Levels of specific IgE own been shown to depend on age, allergen specificity, entire serum IgE, and, with inhalant allergens, the season of the year.15,16

Other limitations of blood testing are its cost and a delay of several days to a week in obtaining the results.17

The allergy evaluation should start with a thorough history to glance for possible triggers for the patient’s symptoms.

For example, respiratory conditions such as asthma and rhinitis may be exacerbated during specific times of the year when certain pollens are commonly present.

What does h mean in allergy test

For patients with this pattern, blood testing for allergy to common inhalants, including pollens, may be appropriate. Similarly, peanut allergy evaluation is indicated for a kid who has suffered an anaphylactic reaction after consuming peanut butter. Blood testing is also indicated in patients with a history of venom anaphylaxis, especially if venom skin testing was negative.

In cases in which the patient does not own a clear history of sensitization, blood testing for allergy to multiple foods may discover evidence of sensitization that does not necessarily correlate with clinical disease.18

Likewise, blood tests are not likely to be clinically relevant in conditions not mediated by IgE, such as food intolerances (eg, lactose intolerance), celiac disease, the DRESS syndrome (drug rash, eosinophilia, and systemic symptoms), Stevens-Johnson syndrome, toxic epidermal necrolysis, or other types of drug hypersensitivity reactions, such as serum sickness.3

Tests for allergy to hundreds of substances are available.

Foods

Milk, eggs, soy, wheat, peanuts, tree nuts, fish, and shellfish account for most cases of food allergy in the United States.18

IgE-mediated hypersensitivity to milk, eggs, and peanuts tends to be more common in children, whereas peanuts, tree nuts, fish, and shellfish are more commonly associated with reactions in adults.18 Children are more likely to outgrow allergy to milk, soy, wheat, and eggs than allergy to peanuts, tree nuts, fish, and shellfish—only about 20% of children outgrow peanut allergy.18

Patients with an IgE-mediated reaction to foods should be closely followed by a specialist, who can best assist determine the appropriateness of additional testing (such as an oral challenge under observation), avoidance recommendations, and the introduction of foods back into the diet.19

Specific IgE tests for allergy to a variety of foods are available and can be extremely useful for diagnosis when used in the appropriate setting.

Double-blind, placebo-controlled studies own established a relationship between quantitative levels of specific IgE and the 95% likelihood of experiencing a subsequent clinical reaction upon exposure to that allergen.

One of the most frequently cited studies is summarized in Table 1.7,8,18 In numerous of these studies the gold standard for food allergy was a positive double-blind, placebo-controlled oral food challenge. Of note, these values predict the likelihood of a clinical reaction but not necessarily its severity.

One caveat about these studies is that numerous were initially performed in children with a history of food allergy, numerous of whom had atopic dermatitis, and the findings own not been systematically reexamined in larger studies in more heterogeneous populations.

For example, at least eight studies tried to identify a diagnostic IgE level for cow’s milk allergy.

The 95% confidence intervals varied widely, depending on the study design, the age of the study population, the prevalence of food allergy in the population, and the statistical method used for analysis.5 For most other foods for which blood tests are available, few studies own been performed to establish predictive values similar to those in Table 1.

Thus, slight elevations in antigen-specific IgE (> 0.35 kU/L) may correlate only with in vitro sensitization in a patient who has no clinical reactivity upon oral exposure to a specific antigen.

Broad food panels own been shown to own false-positive rates higher than 50%—ie, in more than half of cases, positive results own no clinical relevance.

Therefore, these large food panels should not be used for screening.19 Instead, it is recommended that tests be limited to relevant foods based on the patient’s history when evaluating symptoms consistent with an IgE-mediated reaction to a specific food.

Food-specific IgE evaluation is also not helpful in evaluating non-IgE adverse reactions to foods (eg, intolerances).

Therefore, the patient’s history remains the most significant tool for evaluation of food allergy. In cases in which the patient’s history suggests a food-associated IgE-mediated reaction and the blood test is negative, the patient should be referred to a specialist for skin testing with commercial extracts or even unused food extracts, given the higher sensitivity of in vivo testing.20

Immune system response to a substance that most people tolerate well

For the medical journal of this title, see Allergy (journal).

Allergy
Hives are a common allergic symptom
Specialty Immunology
Symptoms Red eyes, itchy rash, runny nose, shortness of breath, swelling, sneezing[1]
Types Hay fever, food allergies, atopic dermatitis, allergic asthma, anaphylaxis[2]
Causes Genetic and environmental factors[3]
Diagnostic method Based on symptoms, skin prick test, blood test[4]
Differential diagnosis Food intolerances, food poisoning[5]
Prevention Early exposure to potential allergens[6]
Treatment Avoiding known allergens, medications, allergen immunotherapy[7]
Medication Steroids, antihistamines, epinephrine, mast cell stabilizers, antileukotrienes[7][8][9][10]
Frequency Common[11]

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[12] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[2] Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling.[1]Food intolerances and food poisoning are separate conditions.[4][5]

Common allergens include pollen and certain foods.[12] Metals and other substances may also cause problems.[12] Food, insect stings, and medications are common causes of severe reactions.[3] Their development is due to both genetic and environmental factors.[3] 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.[13] Diagnosis is typically based on a person’s medical history.[4] Further testing of the skin or blood may be useful in certain cases.[4] Positive tests, however, may not mean there is a significant allergy to the substance in question.[14]

Early exposure to potential allergens may be protective.[6] Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines.[7] In severe reactions injectable adrenaline (epinephrine) is recommended.[8]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.[7] Its use in food allergies is unclear.[7]

Allergies are common.[11] In the developed world, about 20% of people are affected by allergic rhinitis,[15] about 6% of people own at least one food allergy,[4][6] and about 20% own atopic dermatitis at some point in time.[16] Depending on the country about 1–18% of people own asthma.[17][18] Anaphylaxis occurs in between 0.05–2% of people.[19] Rates of numerous allergic diseases appear to be increasing.[8][20] The expression «allergy» was first used by Clemens von Pirquet in 1906.[3]


Cause

Risk factors for allergy can be placed in two general categories, namely host and environmental factors.[31] Host factors include heredity, sex, race, and age, with heredity being by far the most significant.

However, there own 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.[32]

Stress

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.[63]

Medications

Main article: Drug allergy

See also: Adverse drug reaction and Drug eruption

About 10% of people report that they are allergic to penicillin; however, 90% turn out not to be.[45] Serious allergies only happen in about 0.03%.[45]

Insect stings

Main article: Insect sting allergy

Typically, insects which generate allergic responses are either stinging insects (wasps, bees, hornets and ants) or biting insects (mosquitoes, ticks).

Stinging insects inject venom into their victims, whilst biting insects normally introduce anti-coagulants.

Latex

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.[43]

The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction generally lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations.[43]Anaphylactic reactions happen most often in sensitive patients who own been exposed to a surgeon’s latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions.[43]

Latex and banana sensitivity may cross-react.

Furthermore, those with latex allergy may also own sensitivities to avocado, kiwifruit, and chestnut.[44] These people often own perioral itching and local urticaria. Only occasionally own 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.[43]

Genetics

Allergic diseases are strongly familial: identical twins are likely to own the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins.[50] Allergic parents are more likely to own allergic children,[51] 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 own 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.[51]

The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk.[52] Several studies own shown that IgE levels are highest in childhood and drop rapidly between the ages of 10 and 30 years.[52] The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10.[53]

Overall, boys own a higher risk of developing allergies than girls,[51] although for some diseases, namely asthma in young adults, females are more likely to be affected.[54] These differences between the sexes tend to decrease in adulthood.[51]

Ethnicity may frolic a role in some allergies; however, racial factors own been hard to separate from environmental influences and changes due to migration.[51] It has been suggested that diverse genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins.[55]

Toxins interacting with proteins

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.[46] Of these poisonous plants, sumac is the most virulent.[47] The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.[48]

Estimates vary on the percentage of the population that will own an immune system response. Approximately 25 percent of the population will own 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.[49]

Hygiene hypothesis

Main article: Hygiene hypothesis

Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response. Numerous 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.[56] In other words, individuals living in too sterile an environment are not exposed to enough pathogens to hold 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.[57]

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 kid. The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an significant theoretical framework for the study of allergic disorders.

It is used to explain the increase in allergic diseases that own 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 significant modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis. Studies own 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.[58] Longitudinal studies in the third world protest an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner.[59] The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases.[60] 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.[61][62]

Foods

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.[33] Other food allergies, affecting less than 1 person per 10,000 population, may be considered «rare».[34] The use of hydrolysed milk baby formula versus standard milk baby formula does not appear to change the risk.[35]

The most common food allergy in the US population is a sensitivity to crustacea.[34] 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.[33]

Rates of allergies differ between adults and children. Peanut allergies can sometimes be outgrown by children.

What does h mean in allergy test

Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5.[36] The sensitivity is generally to proteins in the white, rather than the yolk.[37]

Milk-protein allergies are most common in children.[38] Approximately 60% of milk-protein reactions are immunoglobulin E-mediated, with the remaining generally attributable to inflammation of the colon.[39] Some people are unable to tolerate milk from goats or sheep as well as from cows, and numerous are also unable to tolerate dairy products such as cheese.

Roughly 10% of children with a milk allergy will own a reaction to beef. Beef contains little amounts of proteins that are present in greater abundance in cow’s milk.[40]Lactose intolerance, a common reaction to milk, is not a form of allergy at every, 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 numerous tree nuts, including pecans, pistachios, pine nuts, and walnuts.[37] Also seeds, including sesame seeds and poppy seeds, contain oils in which protein is present, which may elicit an allergic reaction.[37]

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 unmodified crops.[41][42]

Other environmental factors

There are differences between countries in the number of individuals within a population having allergies. 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.[64] Historically, the trees planted in urban areas were predominantly male to prevent litter from seeds and fruits, but the high ratio of male trees causes high pollen counts.[65]

Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy.[32] 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.[66] 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.[67]

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.[68] 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.[69] This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans 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.[70] In specific, research suggests that allergies may coincide with the delayed establishment of gut flora in infants.[71] 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.[64] Clinical trials own been initiated to test the effectiveness of certain worms in treating some allergies.[72] It may be that the term ‘parasite’ could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work.[72] For more information on this topic, see Helminthic therapy.



What is an allergy blood test?

Allergies are a common and chronic condition that involves the body’s immune system. Normally, your immune system works to fight off viruses, bacteria, and other infectious agents. When you own an allergy, your immune system treats a harmless substance, love dust or pollen, as a threat. To fight this perceived threat, your immune system makes antibodies called immunoglobulin E (IgE).

Substances that cause an allergic reaction are called allergens. Besides dust and pollen, other common allergens include animal dander, foods, including nuts and shellfish, and certain medicines, such as penicillin.

Allergy symptoms can range from sneezing and a stuffy nose to a life-threatening complication called anaphylactic shock. Allergy blood tests measure the quantity of IgE antibodies in the blood. A little quantity of IgE antibodies is normal. A larger quantity of IgE may mean you own an allergy.

Other names: IgE allergy test, Quantitative IgE, Immunoglobulin E, Entire IgE, Specific IgE

This article is about the method for medical diagnosis of allergies.

For other uses, see Scratch test (disambiguation).

Allergy diagnosis

Skin allergy testing or skin prick test is a method for medical diagnosis of allergies that attempts to provoke a little, controlled, allergic response.


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