What allergy test detects allergen specific ige in a blood sample

The market-leading RAST methodology was invented and marketed in by Pharmacia Diagnostics AB, Uppsala, Sweden, and the acronym RAST is actually a brand name. In , Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which literature may also describe as: CAP RAST, CAP FEIA (fluorenzymeimmunoassay), and Pharmacia CAP.

What allergy test detects allergen specific ige in a blood sample

A review of applicable quality assessment programs shows that this new test has replaced the original RAST in approximately 80% of the world’s commercial clinical laboratories, where specific IgE testing is performed. The newest version, the ImmunoCAP Specific IgE , is the only specific IgE assay to get FDA approval to quantitatively report to its detection limit of kU/L. This clearance is based on the CLSI/NCCLSA Limits of Detection and Limits of Quantitation, October guideline.

The guidelines for diagnosis and management of food allergy issues by the National Institute of Health state that:

In the United States National Institute of Allergy and Infectious Diseases recommended that the RAST measurements of specific immunoglobulin E for the diagnosis of allergy be abandoned in favor of testing with more sensitive fluorescence enzyme-labeled assays.[13]


Medical uses

The two most commonly used methods of confirming allergen sensitization are skin testing and allergy blood testing.

Both methods are recommended by the NIH guidelines and own similar diagnostic worth in terms of sensitivity and specificity.[1][2]

Advantages of the allergy blood test range from: excellent reproducibility across the full measuring range of the calibration curve, it has extremely high specificity as it binds to allergen specific IgE, and extremely sensitive too, when compared with skin prick testing. In general, this method of blood testing (in-vitro, out of body) vs skin-prick testing (in-vivo, in body) has a major advantage: it is not always necessary to remove the patient from an antihistamine medication regimen, and if the skin conditions (such as eczema) are so widespread that allergy skin testing cannot be done.

Allergy blood tests, such as ImmunoCAP, are performed without procedure variations, and the results are of excellent standardization.[3]

Adults and children of any age can take an allergy blood test. For babies and extremely young children, a single needle stick for allergy blood testing is often more tender than several skin tests. However, skin testing techniques own improved. Most skin testing does not involve needles and typically skin testing results in minimal patient discomfort.

Drawbacks to RAST and ImmunoCAP techniques do exist. Compared to skin testing, ImmunoCAP and other RAST techniques take longer to act out and are less cost effective.[4] Several studies own also found these tests to be less sensitive than skin testing for the detection of clinically relevant allergies.[5] Untrue positive results may be obtained due to cross-reactivity of homologous proteins or by cross-reactive carbohydrate determinants (CCDs).[6]

In the NIH food guidelines issued in December it was stated that “The predictive values associated with clinical evidence of allergy for ImmunoCAP cannot be applied to other test methods.”[7] With over scientific articles using ImmunoCAP and showing its clinical worth, ImmunoCAP is perceived as “Gold standard” for in vitro IgE testing[8][9]


Method

The RAST is a radioimmunoassay test to detect specific IgE antibodies to suspected or known allergens for the purpose of guiding a diagnosis about allergy.[10][11] IgE is the antibody associated with Type I allergic response: for example, if a person exhibits a high level of IgE directed against pollen, the test may indicate the person is allergic to pollen (or pollen-like) proteins.

A person who has outgrown an allergy may still own a positive IgE years after exposure.

The suspected allergen is bound to an insoluble material and the patient’s serum is added. If the serum contains antibodies to the allergen, those antibodies will bind to the allergen. Radiolabeled anti-human IgE antibody is added where it binds to those IgE antibodies already bound to the insoluble material. The unbound anti-human IgE antibodies are washed away. The quantity of radioactivity is proportional to the serum IgE for the allergen.[12]

RASTs are often used to test for allergies when:

  1. a patient suffers from severe skin conditions such as widespread eczema or
  2. a physician advises against the discontinuation of medications that can interfere with test results or cause medical complications;
  3. a patient has such a high sensitivity level to suspected allergens that any istration of those allergens might result in potentially serious side effects.


External links

  • Cardiovascular (eg, tachycardia, hypotension)
  • ^UpToDate (?source=search_result&search=skin+testing&selectedTitle=1~)
  • ^Boyce J et al.

    Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of

  • Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  • ^NIH Guidelines for the Diagnosis and Management of Food Allergy in the United States. Report of the NIAID- Sponsored Expert Panel, , NIH Publication no.
  • ^Wang J, Godbold JH, Sampson HA (). «Correlation of serum allergy (IgE) tests performed by diverse assay systems». J. Allergy Clin. Immunol.

    (5): – doi/ PMID

  • ^Wood R; et al. (). «Accuracy of IgE antibody laboratory results». Ann Allergy Asthma Immunol. 99 (1): 34– doi/s(10) PMID
  • ^NIAID-Sponsored Expert Panel (December ). «Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel». The Journal of Allergy and Clinical Immunology. (6): S1–S doi/ PMC PMID Retrieved 30 August
  • Cutaneous (eg, acute urticaria, angioedema)
  • Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

  • Immulite (Siemens AG, Berlin, Germany)
  • ^American Academy of Allergy, Asthma, and Immunology, «Five Things Physicians and Patients Should Question»(PDF), Choosing Wisely: an initiative of the ABIM Foundation, American Academy of Allergy, Asthma, and Immunology, retrieved August 14, CS1 maint: multiple names: authors list (link)
  • Gastrointestinal (eg, vomiting, diarrhea)
  • ^WebMD > Medical Dictionary > radioallergosorbent test (RAST) Citing: Stedman’s Medical Dictionary 28th Edition.

    Copyright

  • ImmunoCAP (Phadia AB, Uppsala, Sweden)
  • ^Cox, L.; Williams, B.; Sicherer, S.; Oppenheimer, J.; Sher, L.; Hamilton, R.; Golden, D.

    What allergy test detects allergen specific ige in a blood sample

    (). «Pearls and pitfalls of allergy diagnostic testing: Report from the American College of Allergy, Asthma and Immunology/American Academy of Allergy, Asthma and Immunology Specific IgE Test Task Force». Annals of Allergy, Asthma & Immunology. (6): – doi/S(10) PMID

  • ^Cox, L. Overview of Serological-Specific IgE Antibody Testing in Children. Pediatric Allergy and Immunology.
  • ^Chinoy B, Yee E, Bahna SL. Skin testing versus radioallergosorbent testing for indoor allergens. Clin Mol Allergy. Apr 15;3(1)
  • ^Hamilton R et al. Proficiency Survey-Based Evaluation of Clinical Entire and Allergen-Specific IgE Assay Performance.

    Arch Pathol Lab Med. ; –

  • ^Holzweber, F. (). «Inhibition of IgE binding to cross-reactive carbohydrate determinants enhances diagnostic selectivity». Allergy. 68 (10): – doi/all PMC PMID
  • HYTEC (Hycor/Agilent, Garden Grove, CA).

Health care providers often need to assess allergic disorders such as allergic rhinoconjunctivitis, asthma, and allergies to foods, drugs, latex, and venom, both in the hospital and in the clinic.

Unfortunately, some symptoms, such as chronic nasal symptoms, can happen in both allergic and nonallergic disorders, and this overlap can confound the diagnosis and therapy.

Studies propose that when clinicians use the history and physical examination alone in evaluating possible allergic disease, the accuracy of their diagnoses rarely exceeds 50%.1

Blood tests are now available that measure immunoglobulin E (IgE) directed against specific antigens. These in vitro tests can be significant tools in assessing a patient whose history suggests an allergic disease.2 However, neither allergy skin testing nor these blood tests are intended to be used for screening: they may be most useful as confirmatory diagnostic tests in cases in which the pretest clinical impression of allergic disease is high.

In susceptible people, IgE is produced by B cells in response to specific antigens such as foods, pollens, latex, and drugs.

This antigen-specific (or allergen-specific) IgE circulates in the serum and binds to high-affinity IgE receptors on immune effector cells such as mast cells located throughout the body.

Upon subsequent exposure to the same allergen, IgE receptors cross-link and initiate downstream signaling events that trigger mast cell degranulation and an immediate allergic response—hence the term immediate (or Gell-Coombs type I) hypersensitivity.3

Common manifestations of type I hypersensitivity reactions include signs and symptoms that can be:

  1. Cardiovascular (eg, tachycardia, hypotension)
  2. Cutaneous (eg, acute urticaria, angioedema)
  3. Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  4. Gastrointestinal (eg, vomiting, diarrhea)
  5. Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

The blood tests for allergic disease are immunoassays that measure the level of IgE specific to a specific allergen. The tests can be used to assess sensitivity to various allergens, for example, to common inhalants such as dust mites and pollens and to foods, drugs, venom, and latex.

Types of immunoassays include enzyme-linked immunosorbent assays (ELISAs), fluorescent enzyme immunoassays (FEIAs), and radioallergosorbent assays (RASTs).

At present, most commercial laboratories use one of three autoanalyzer systems to measure specific IgE:

  1. Immulite (Siemens AG, Berlin, Germany)
  2. ImmunoCAP (Phadia AB, Uppsala, Sweden)
  3. HYTEC (Hycor/Agilent, Garden Grove, CA).

These systems use a solid-phase polymer (cellulose or avidin) in which the antigen is embedded. The polymer also facilitates binding of IgE and, therefore, increases the sensitivity of the test.5 Specific IgE from the patient’s serum binds to the allergen embedded in the polymer, and then unbound antibodies are washed off.

Despite the term “RAST,” these systems do not use radiation.

A fluorescent antibody is added that binds to the patient’s IgE, and the quantity of IgE present is calculated from the quantity of fluorescence.6 Results are reported in kilounits of antibody per liter (kU/L) or nanograms per milliliter (ng/mL).5–7

In general, the sensitivity of these tests ranges from 60% to 95% and their specificity from 30% to 95%, with a concordance among diverse immunoassays of 75% to 90%.8

Levels of IgE for a specific allergen are also divided into semiquantitative classes, from class I to class V or VI. In general, class I and class II correlate with a low level of allergen sensitization and, often, with a low likelihood of a clinical reaction.

On the other hand, classes V and VI reflect higher degrees of sensitization and generally correlate with IgE-mediated clinical reactions upon allergen exposure.

The interpretation of a positive (ie, “nonzero”) test result must be individualized on the basis of clinical presentation and risk factors. A specialist can make an significant contribution by helping to interpret any positive test result or a negative test result that does not correlate with the patient’s history.

Allergy blood testing is convenient, since it involves only a standard blood draw.

In theory, allergy blood testing may be safer, since it does not expose the patient to any allergens.

On the other hand, numerous patients experience bruising from venipuncture performed for any reason: 16% in one survey.9 In another survey,10 adverse reactions of any type occurred in % of patients undergoing venipuncture but only in % of those undergoing allergy skin testing. Therefore, allergy blood testing may be most appropriate in situations in which a patient’s history suggests that he or she may be at risk of a systemic reaction from a traditional skin test or in cases in which skin testing is not possible (eg, extensive eczema).

Another advantage of allergy blood testing is that it is not affected by drugs such as antihistamines or tricyclic antidepressants that suppress the histamine response, which is a problem with skin testing.

Allergy blood testing may also be useful in patients on long-term glucocorticoid therapy, although the data conflict.

Prolonged oral glucocorticoid use is associated with a decrease in mast cell density and histamine content in the skin,11,12 although in one study a corticosteroid was found not to affect the results of skin-prick testing for allergy.13 Thus, allergy blood testing can be performed in patients who own severe eczema or dermatographism or who cannot safely suspend taking antihistamines or tricyclic antidepressants.

Health care providers often need to assess allergic disorders such as allergic rhinoconjunctivitis, asthma, and allergies to foods, drugs, latex, and venom, both in the hospital and in the clinic.

Unfortunately, some symptoms, such as chronic nasal symptoms, can happen in both allergic and nonallergic disorders, and this overlap can confound the diagnosis and therapy.

Studies propose that when clinicians use the history and physical examination alone in evaluating possible allergic disease, the accuracy of their diagnoses rarely exceeds 50%.1

Blood tests are now available that measure immunoglobulin E (IgE) directed against specific antigens. These in vitro tests can be significant tools in assessing a patient whose history suggests an allergic disease.2 However, neither allergy skin testing nor these blood tests are intended to be used for screening: they may be most useful as confirmatory diagnostic tests in cases in which the pretest clinical impression of allergic disease is high.

In susceptible people, IgE is produced by B cells in response to specific antigens such as foods, pollens, latex, and drugs.

This antigen-specific (or allergen-specific) IgE circulates in the serum and binds to high-affinity IgE receptors on immune effector cells such as mast cells located throughout the body.

Upon subsequent exposure to the same allergen, IgE receptors cross-link and initiate downstream signaling events that trigger mast cell degranulation and an immediate allergic response—hence the term immediate (or Gell-Coombs type I) hypersensitivity.3

Common manifestations of type I hypersensitivity reactions include signs and symptoms that can be:

  1. Cardiovascular (eg, tachycardia, hypotension)
  2. Cutaneous (eg, acute urticaria, angioedema)
  3. Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  4. Gastrointestinal (eg, vomiting, diarrhea)
  5. Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

The blood tests for allergic disease are immunoassays that measure the level of IgE specific to a specific allergen. The tests can be used to assess sensitivity to various allergens, for example, to common inhalants such as dust mites and pollens and to foods, drugs, venom, and latex.

Types of immunoassays include enzyme-linked immunosorbent assays (ELISAs), fluorescent enzyme immunoassays (FEIAs), and radioallergosorbent assays (RASTs).

At present, most commercial laboratories use one of three autoanalyzer systems to measure specific IgE:

  1. Immulite (Siemens AG, Berlin, Germany)
  2. ImmunoCAP (Phadia AB, Uppsala, Sweden)
  3. HYTEC (Hycor/Agilent, Garden Grove, CA).

These systems use a solid-phase polymer (cellulose or avidin) in which the antigen is embedded. The polymer also facilitates binding of IgE and, therefore, increases the sensitivity of the test.5 Specific IgE from the patient’s serum binds to the allergen embedded in the polymer, and then unbound antibodies are washed off.

Despite the term “RAST,” these systems do not use radiation.

A fluorescent antibody is added that binds to the patient’s IgE, and the quantity of IgE present is calculated from the quantity of fluorescence.6 Results are reported in kilounits of antibody per liter (kU/L) or nanograms per milliliter (ng/mL).5–7

In general, the sensitivity of these tests ranges from 60% to 95% and their specificity from 30% to 95%, with a concordance among diverse immunoassays of 75% to 90%.8

Levels of IgE for a specific allergen are also divided into semiquantitative classes, from class I to class V or VI.

In general, class I and class II correlate with a low level of allergen sensitization and, often, with a low likelihood of a clinical reaction. On the other hand, classes V and VI reflect higher degrees of sensitization and generally correlate with IgE-mediated clinical reactions upon allergen exposure.

The interpretation of a positive (ie, “nonzero”) test result must be individualized on the basis of clinical presentation and risk factors. A specialist can make an significant contribution by helping to interpret any positive test result or a negative test result that does not correlate with the patient’s history.

Allergy blood testing is convenient, since it involves only a standard blood draw.

In theory, allergy blood testing may be safer, since it does not expose the patient to any allergens.

On the other hand, numerous patients experience bruising from venipuncture performed for any reason: 16% in one survey.9 In another survey,10 adverse reactions of any type occurred in % of patients undergoing venipuncture but only in % of those undergoing allergy skin testing. Therefore, allergy blood testing may be most appropriate in situations in which a patient’s history suggests that he or she may be at risk of a systemic reaction from a traditional skin test or in cases in which skin testing is not possible (eg, extensive eczema).

Another advantage of allergy blood testing is that it is not affected by drugs such as antihistamines or tricyclic antidepressants that suppress the histamine response, which is a problem with skin testing.

Allergy blood testing may also be useful in patients on long-term glucocorticoid therapy, although the data conflict.

Prolonged oral glucocorticoid use is associated with a decrease in mast cell density and histamine content in the skin,11,12 although in one study a corticosteroid was found not to affect the results of skin-prick testing for allergy.13 Thus, allergy blood testing can be performed in patients who own severe eczema or dermatographism or who cannot safely suspend taking antihistamines or tricyclic antidepressants.



en españolAnálisis de sangre: inmunoglobulina E (IgE)

Can I Stay With My Kid During an IgE Test?

Parents generally can stay with their kid during a blood test.

Urge your kid to relax and stay still because tensing muscles can make it harder to draw blood. Your kid might desire to glance away when the needle is inserted and the blood is collected.

What allergy test detects allergen specific ige in a blood sample

Assist your kid to relax by taking slow deep breaths or singing a favorite song.

How Is an IgE Test Done?

Most blood tests take a little quantity of blood from a vein. To do that, a health professional will:

  1. insert a needle into a vein (usually in the arm inside of the elbow or on the back of the hand)
  2. clean the skin
  3. put an elastic band (tourniquet) above the area to get the veins to swell with blood
  4. pull the blood sample into a vial or syringe
  5. take off the elastic band and remove the needle from the vein

In babies, blood draws are sometimes done as a «heel stick collection.» After cleaning the area, the health professional will prick your baby’s heel with a tiny needle (or lancet) to collect a little sample of blood.

Collecting a sample of blood is only temporarily uncomfortable and can feel love a quick pinprick.

What Happens After an IgE Test?

The health professional will remove the elastic band and the needle and cover the area with cotton or a bandage to stop the bleeding.

Afterward, there may be some mild bruising, which should go away in a few days.

What Happens After an IgE Test?

The health professional will remove the elastic band and the needle and cover the area with cotton or a bandage to stop the bleeding. Afterward, there may be some mild bruising, which should go away in a few days.

What Is a Blood Test?

A blood test is when a sample of blood is taken from the body to be tested in a lab.

Doctors order blood tests to check things such as the levels of glucose, hemoglobin, or white blood cells. This can assist them detect problems love a disease or medical condition. Sometimes, blood tests can assist them see how well an organ (such as the liver or kidneys) is working.

Are There Any Risks From IgE Tests?

An IgE test is a safe procedure with minimal risks. Some kids might feel faint or lightheaded from the test. A few kids and teens own a strong fear of needles. If your kid is anxious, talk with the doctor before the test about ways to make the procedure easier.

A little bruise or mild soreness around the blood test site is common and can final for a few days.

Get medical care for your kid if the discomfort gets worse or lasts longer.

If you own questions about the IgE test, speak with your doctor or the health professional doing the blood draw.

en españolAnálisis de sangre: inmunoglobulina E (IgE) alérgeno específico

When Are IgE Test Results Ready?

Blood samples are processed by a machine, and it may take a few days for the results to be available. If the test results show signs of a problem, the doctor might order other tests to figure out what the problem is and how to treat it.

How Is an IgE Test Done?

Most blood tests take a little quantity of blood from a vein.

To do that, a health professional will:

  1. insert a needle into a vein (usually in the arm inside of the elbow or on the back of the hand)
  2. clean the skin
  3. put an elastic band (tourniquet) above the area to get the veins to swell with blood
  4. pull the blood sample into a vial or syringe
  5. take off the elastic band and remove the needle from the vein

In babies, blood draws are sometimes done as a «heel stick collection.» After cleaning the area, the health professional will prick your baby’s heel with a tiny needle (or lancet) to collect a little sample of blood.

Collecting a sample of blood is only temporarily uncomfortable and can feel love a quick pinprick.

How Endless Does an IgE Test Take?

Most blood tests take just a few minutes.

Occasionally, it can be hard to discover a vein, so the health professional may need to attempt more than once.

Are There Any Risks From IgE Tests?

An IgE test is a safe procedure with minimal risks. Some kids might feel faint or lightheaded from the test. A few kids and teens own a strong fear of needles. If your kid is anxious, talk with the doctor before the test about ways to make the procedure easier.

A little bruise or mild soreness around the blood test site is common and can final for a few days. Get medical care for your kid if the discomfort gets worse or lasts longer.

If you own questions about the IgE test, speak with your doctor or the health professional doing the blood draw.

IgE in Clinical Allergy and Allergy Diagnosis

Updated: July
Originally Posted: May

Updated by:
Jay Portnoy, MD
Professor of Pediatrics
University of Missouri-Kansas City School of Medicine
Division Director of Allergy, Asthma & Immunology
Children's Mercy Hospital & Clinics
Kansas City, MO, USA

The role of IgE in allergic inflammation

Allergy Skin Tests

Prick skin tests can be used to identify specific IgE sensitization.

The skin is marked for testing with a panel of appropriate allergens for the patient, selected on the basis of the clinical history and knowledge of the allergens commonly found in the locality. Positive and negative comparator tests using histamine and saline also should be performed to prove that the skin is capable of demonstrating a positive reaction and to prevent the interpretation of false-positive results occurring as a result of dermatographism.

A variety of methods can used to act out a prick skin test.

In one method, a drop of allergen solution is placed onto the skin at each mark, and a unused fine sterile needle or lancet is used to gently prick the skin through each drop, introducing a minute volume of allergen solution into the dermis. Another method uses a plastic pricking device that delivers a specific quantity of allergen to the skin. These can be combined into multiple prickers so that numerous tests can be applied at one time. After minutes the results are interpreted by reference to the control tests. Provided that there is no wheal response to the negative control, the presence of a raised wheal at the site of the allergen skin prick test of 3 mm or greater in diameter indicates the presence of IgE antibodies specific to that allergen.

When interpreted in conjunction with the clinical history, the results of skin prick testing can confirm a diagnosis of IgE-mediated disease and identify causal allergens. Skin prick tests are particularly dependable for inhalant allergens. However, the variations in reaction between tests and testers limits it use to experienced personnel. To see a video demonstration of skin prick testing click here.

Re-exposure to allergen

Upon re-exposure, binding of the allergen to IgE orchestrates the immune system to initiate a more aggressive and rapid memory response. Cross-linking of a sufficient number of mast cell/basophil-bound IgE antibodies by allergen initiates a process of intra-cellular signaling, which leads to degranulation of cells, with the release of mediators of inflammation.

Mast cells attempt to sustain a fixed number of unoccupied high-affinity IgE receptors on their cell surface. IgE antibodies bind to these receptor sites, waiting for their specific allergen to be encountered. To hold the number of unoccupied IgE receptor sites constant the mast cell regulates IgE receptor expression, probably in response to the levels of circulating IgE.

IgE and the nomenclature of allergic disease

The understanding of the immunological mechanisms underlying allergic disease has led to a revised nomenclature, which relates clinical symptoms to the initiating immunological mechanism.

The essence of this new nomenclature can be found in several language translations on the European Academy of Allergology and Clinical Immunology's website. To review the full document click here.

Allergy is defined as "a hypersensitivity reaction mediated by immunological mechanisms" which can be antibody- or cell-mediated. In the majority of cases the antibody typically responsible for an allergic reaction belongs to the IgE isotype and individuals may be referred to as suffering from an IgE-mediated allergic disease, eg, IgE-mediated asthma.

Atopy is a personal or familial tendency to produce IgE antibodies in response to low doses of allergens, generally proteins, and, as a consequence, to develop typical symptoms of asthma, rhinoconjunctivitis or allergic skin disease. What is generally known as "atopic eczema/dermatitis" is not one, single disease but rather an aggregation of several diseases with certain clinical characteristics in common, and the term atopic eczema/dermatitis syndrome (AEDS) has been proposed.

The subgroup related to allergic asthma and rhinoconjunctivitis, the IgE-associated subgroup of AEDS, can appropriately be called atopic dermatitis/atopic eczema.

What Is a Blood Test?

A blood test is when a sample of blood is taken from the body to be tested in a lab. Doctors order blood tests to check things such as the levels of glucose, hemoglobin, or white blood cells. This can assist them detect problems love a disease or medical condition. Sometimes, blood tests can assist them see how well an organ (such as the liver or kidneys) is working.

When Are IgE Test Results Ready?

Blood samples are processed by a machine, and it may take a few days for the results to be available.

If the test results show signs of a problem, the doctor might order other tests to figure out what the problem is and how to treat it.

Introduction

In a physician observed, following a blood transfusion, a case of transient asthma caused by allergy to horse dander. This was the first indication of a factor in blood capable of mediating an allergic reaction. In Prausnitz & Küstner performed the passive transfer of this substance to artificially induce a positive skin test. The search for reagin started after that, but until the 's it was thought that reaginic activity was not a single, indivisible molecular species but was present in allergic sera in the form of labile complexes.

This differed radically from immune antibodies that were known at the time.

In-vitro tests for specific IgE antibodies.

The discovery of IgE allowed the development of immuno-assays for IgE and IgE-antibodies, enabling direct and objective measurement of the extent and specificity of the immune response. Immunoassays such as RAST (radio allergosorbent assay),, Quick (fluorescent allergosorbant test) and ELISA (enzyme-linked immunosorbant assay) own been developed each using a diverse detection system.

For each assay, allergens are linked to paper discs or polyurethane caps (ImmunoCAP) and are incubated with the individual's serum. Binding of IgE specific to allergens is detected by the use of an enzyme linked anti-human IgE antibody leading either to a colorimetric or fluorescent product that can be measured. There is a excellent correlation between the results of serum tests for IgE antibodies, and positive skin and provocation tests, as well as symptoms of allergy.

Positive in-vitro results to a specific allergen protest IgE sensitization but are not proof that the allergen is the cause of clinical symptoms.

The measurement of allergen specific IgE antibodies in serum is of similar diagnostic worth to that of skin tests but has a much higher reproducibility and is not influenced by ongoing symptoms or treatment, eg, antihistamines or anti-inflammatory therapy. In some instances, especially in food allergic individuals where, in rare cases, even skin prick testing with minute amounts of allergen might cause an anaphylactic reaction, in-vitro tests using blood samples is a safe method to determine levels of specific IgE antibodies.

What allergy test detects allergen specific ige in a blood sample

In-vitro tests are also preferred for individuals who own widespread eczema, which precludes skin prick testing.

Approximately diverse allergens are now available for in-vitro-based allergy diagnosis. In addition to classical pollen, dander and food allergens, drugs, occupational chemicals and recombinant allergens are available. The general availability of well standardized in-vitro allergy tests has greatly improved the quality of allergy diagnosis.

Identification of elevated entire IgE as opposed to specific IgE, in serum, secretion or on cell surfaces is of little diagnostic worth.

The reason is that mitogenic factors in viruses (e.g., Cytomegalovirus — CMV), bacteria (e.g., Staphylococcus), helminths (e.g., Ascaris, Schistosoma) and adjuvant factors in air pollution (e.g., cigarette smoke, and diesel exhaust) stimulate the production of IgE molecules without initiating any allergen specific IgE-sensitization. However, production of IgE-antibodies will increase the entire IgE level slightly and thus an increased total-IgE in cord blood is a high sensitivity but low specificity predictor of allergy. A extremely low entire IgE, on the other hand, indicates a low probability of specific IgE sensitization.

Sensitization

The immune response in allergy begins with sensitization.

When, for example, home dust mite or pollen allergens are inhaled, antigen presenting cells in the epithelium lining of the airways of the lungs and nose, internalise, process and then express these allergens on their cell surface. The allergens are then presented to other cells involved in the immune response, particularly T-lymphocytes. Through a series of specific cell interactions B-lymphocytes are transformed into antibody secretory cells — plasma cells. In the allergic response, the plasma cell produces IgE-antibodies, which, love antibodies of other immunoglobulin isotypes, are capable of binding a specific allergen via its Fab portion. Diverse allergens stimulate the production of corresponding allergen-specific IgE antibodies.

Once formed and released into the circulation, IgE binds, through its Fc portion, to high affinity receptors on mast cells, leaving its allergen specific receptor site available for future interaction with allergen. Other cells known to express high-affinity receptors for IgE include basophils, Langerhans cells and activated monocytes. Production of allergen specific IgE-antibodies completes the immune response known as sensitization.

A new immunoglobulin

In the Ishizaka group in Denver, Colorado, USA, reported on an antiserum that could interfere with reaginic activity.

This factor, postulated to represent a new immunoglobulin, was provisionally called yE-globulin. Despite numerous attempts, the group was unable to purify the yE-globulin, which is now known to be present in extremely low concentrations in serum.

Independently of this work, Bennich and Johansson, in , discovered a new class of immunoglobulins, provisionally called IgND. An atypical myeloma protein was found that shared the known physicochemical properties of reagin. It was shown that the PK reaction could be blocked in a dose-dependent way with isolated IgND or Fc fragments of the ND protein. Using radioimmunoassays, a normal counterpart could be detected in serum of healthy individuals and it was found that patients with allergic asthma had on average a sixfold higher concentration of IgND than normals or patients with non-allergic asthma.

A new radioimmunoassay was developed, the radioallergosorbent test (RAST), capable of detecting allergen-specific IgND antibodies to allergen, and their presence in serum correlated with skin test results.

Reagents were exchanged between the laboratories in the USA and Sweden in It was found that antiserum to yE-globulin reacted with isolated ND protein, and that purified ND protein could block the reaction of anti-yE-globulin in a biological test system for reaginic activity.

At the WHO Immunoglobulin Reference Centre in Lausanne, Switzerland in February the researchers from the two groups met, and it was agreed that the data available on the unique structure, antigenic properties and biological activity of IgND, supported by data on yE-globulin, would permit for the declaration of a new immunoglobulin, which was called IgE.

IgE — a beneficial or pathological molecule?

Based upon the observation that allergic responses typically affect the skin, gut, and respiratory tract, the major sites of parasitic invasion, it is thought that IgE evolved as a defense mechanism against parasitic infestation.

Helminths stimulate a vigorous IgE production, including parasite-specific IgE antibody. However, another hypothesis for the beneficial function of IgE antibodies is that they frolic a key role in extremely early recognition of foreign material ("gate keeper function") or a general potentiation of the immune system response by improved antigen presentation. Actually, allergy triggered by IgE may provide a beneficial function to the host; the typical allergic reactions of mucus secretion, sneezing, itching, coughing, bronchoconstriction, tear production, inflammation, vomiting and diarrhoea are every mechanisms that expel allergenic proteins from the body.

Clinical and Laboratory Tests for the Detection of Allergen Specific IgE antibodies

Radioallergosorbent tests (RAST)

The discovery of IgE allowed the development of immuno-assays for IgE and IgE-antibodies, enabling direct and objective measurement of the extent and specificity of the immune response.

In RAST, allergens are linked to paper discs or polyurethane caps (CAP — RAST) and are reacted with the individual's serum. Binding of IgE specific to that allergen is detected by the use of an enzyme linked anti-human IgE antibody in a colorimetric reaction. Results of RAST testing show a extremely excellent corelation between the presence of IgE antibody in serum and positive skin and provocation tests, as well as symptoms of allergy.

Positive RAST results to a specific allergen protest specific IgE sensitization but are not proof that the allergen is the cause of clinical symptoms.

The measurement of allergen specific IgE antibodies in serum is of similar diagnostic worth to that of skin tests but has a much higher reproducibility and is not influenced by ongoing symptoms or treatment, eg, antihistamines or anti-inflammatory therapy. In some instances, especially in food allergic individuals where, in rare cases, even skin prick testing with minute amounts of allergen might cause an anaphylactic reaction, RAST using blood samples is a safe method to determine levels of specific IgE antibodies.

RAST is also the test of choice for individuals who own widespread eczema, which precludes skin prick testing.

Approximately diverse allergens are now available for RAST-based allergy diagnosis. In addition to classical pollen, dander and food allergens, drugs, occupational chemicals and recombinant allergens are available. The general availability of well standardized in-vitro allergy tests has greatly improved the quality of allergy diagnosis.

Measurement of entire IgE, not IgE antibodies, in serum, secretion or on cell surfaces is of little diagnostic worth. The reason is that mitogenic factors in viruses (e.g., Cytomegalovirus — CMV), bacteria (e.g., Staphylococcus), helminths (e.g., Ascaris, Schistosoma) and adjuvant factors in air pollution (e.g., cigarette smoke, and diesel exhaust) stimulate the production of IgE molecules without initiating any allergen specific IgE-sensitization.

However, production of IgE-antibodies will increase the entire IgE level slightly and thus an increased total-IgE in cord blood is a high sensitivity but low specificity predictor of allergy.

The role of atopy in the development of allergic disease

Individuals with a family history of atopy own an increased risk of developing IgE sensitization, and the atopic constitution is also a major risk factor for the development of allergic diseases such allergic asthma, rhinitis or atopic dermatitis/atopic eczema. The contribution of genetic factors to the development of IgE sensitization and to family history of an IgE-mediated disease is between %.

The risk of developing allergic disease in a specific organ is related to family history of that organ-based disease.

Early signs of allergic disease, especially the atopic dermatitis/atopic eczema, and the presence of IgE antibodies specific to inhalant allergens, are significant risk factors for later respiratory allergy. IgE antibodies in infant's serum to basic food proteins, e.g., hen's egg, may be predictive of the 'atopic march' (atopic dermatitis/atopic eczema followed by allergic rhinitis and/or asthma).

Early and tardy phase reactions

The immune system's response to allergen exposure can be divided into two phases.

The first is immediate hypersensitivity or the early phase reaction, which occurs within 15 minutes of exposure to the allergen. The second, or tardy phase reaction, occurs hours after the disappearance of the first phase symptoms and can final for days or even weeks. During the early phase reaction chemical mediators released by mast cells including histamine, prostaglandins, leukotrienes and thromboxane produce local tissue responses characteristic of an allergic reaction. In the respiratory tract for example, these include sneezing, oedema and mucus secretion, with vasodilatation in the nose, leading to nasal blockage, and bronchoconstriction in the lung, leading to wheezing.

During the tardy phase reaction in the lung, cellular infiltration, fibrin deposition and tissue destruction resulting from the sustained allergic response lead to increased bronchial reactivity, oedema and further inflammatory cell recruitment. These observations propose that IgE is instrumental in the immune system's response to allergens by virtue of its ability to trigger mast cell mediator release, leading directly to both the early and tardy phase reactions.

To see a video of the IgE-mediated allergic response click here.

Can IgE sensitization be prevented?

The mechanisms of primary sensitization are still essentially unknown.

Avoidance of allergen exposure has only partially been successful in prevention of IgE-sensitization. Avoidance is hard to implement and can severely restrict lifestyle, benefits are little, and long-term effects are doubtful. Until recently it has been recommended that infants at high allergy risk may benefit through avoidance of pets and dust mites during the first year of life, but new research suggests that in some individuals, exposure to furry animals (but not to dust mites or cockroaches) may result in immunological tolerance rather than immunological sensitization.

A similar finding has been found recently for early introduction of peanut as a way to prevent peanut sensitization in at-risk infants.

Some early respiratory infections, e.g., pertussis and Respiratory Syncitial Virus (RSV) bronchiolitis as well as some forms of gastroenteritis, may enhance IgE-sensitization and thus enhance allergic diseases, although relative lack of early microbial exposure (both gastrointestinal and respiratory) may also enhance the development of allergic diseases. Prevention of IgE sensitization is possible in the occupational environment by the elimination of sensitizing agents from the workplace or implementing measures to prevent employee exposure.

Smoking has been shown to be a risk factor for the development of IgE antibodies against occupational agents and has an adjuvant effect with irritant gases, such as ozone and sulphur. So apart from other benefits to health, non-smoking policies in the workplace may own a role to frolic in preventing IgE sensitization.

How Should We Prepare for an IgE Test?

Your kid should be capable to eat and drink normally unless also getting other tests that require fasting beforehand. Tell your doctor about any medicines your kid takes because some drugs might affect the test results.

Wearing a T-shirt or short-sleeved shirt for the test can make things easier for your kid, and you also can bring along a toy or book as a distraction.

What Is an Immunoglobulin E Test?

An immunoglobulin E (IgE) test measures the level of IgE, a type of antibody.

Antibodies are made by the immune system to protect the body from bacteria, viruses, and allergens. IgE antibodies are normally found in little amounts in the blood, but higher amounts can be a sign that the body overreacts to allergens. This can lead to an allergic reaction.

IgE levels can also be high when the body is fighting off an infection from a parasite or with some immune system conditions.

How Endless Does an IgE Test Take?

Most blood tests take just a few minutes.

Occasionally, it can be hard to discover a vein, so the health professional may need to attempt more than once.

How Should We Prepare for an IgE Test?

Your kid should be capable to eat and drink normally unless also getting other tests that require fasting beforehand. Tell your doctor about any medicines your kid takes because some drugs might affect the test results.

Wearing a T-shirt or short-sleeved shirt for the test can make things easier for your kid, and you also can bring along a toy or book as a distraction.

Can I Stay With My Kid During an IgE Test?

Parents generally can stay with their kid during a blood test.

Urge your kid to relax and stay still because tensing muscles can make it harder to draw blood. Your kid might desire to glance away when the needle is inserted and the blood is collected. Assist your kid to relax by taking slow deep breaths or singing a favorite song.

Why Are IgE Tests Done?

An IgE test may be done if a kid has signs of a possible allergy, immune system problem, or infection with a parasite.

Why Are IgE Tests Done?

An allergen-specific IgE test may be done to glance for some kinds of allergies.

These include types of food, animal dander, pollen, mold, medicine, dust mites, latex, or insect venom.

What Is an Allergen-Specific Immunoglobulin E Test?

An allergen-specific immunoglobulin E (IgE) test measures the levels of diverse IgE antibodies. Antibodies are made by the immune system to protect the body from bacteria, viruses, and allergens. IgE antibodies are normally found in little amounts in the blood, but higher amounts can be found when the body overreacts to allergens.

IgE antibodies are diverse depending on what they react to. An allergen-specific IgE test can show what the body is reacting to.

Summary

A fairly excellent knowledge exists about the various steps in the allergic reaction, but despite present knowledge, the prevalence of allergic diseases is still increasing.

In some areas of the industrialized world up to 50% of the population is affected.

What allergy test detects allergen specific ige in a blood sample

More efforts must be dedicated to the understanding of allergic sensitization and how it can be prevented. The identification of the pathological role of IgE and the subsequent release of inflammatory mediators and cytokines has enabled physicians to treat allergic symptoms with regard to the underlying immunological mechanisms.

What allergy test detects allergen specific ige in a blood sample

New pharmacotherapy in the form of a humanized monoclonal anti-IgE antibody designed to eliminate IgE may own a valuable role in treating IgE sensitized individuals.

A radioallergosorbent test (RAST) is a blood test using radioimmunoassay test to detect specific IgE antibodies, to determine the substances a subject is allergic to. This is diverse from a skin allergy test, which determines allergy by the reaction of a person’s skin to diverse substances.

Because there are other tests that assist with confirmation, results are best interpreted by a doctor.


Scale

The RAST is scored on a scale from 0 to 6:

RAST rating IgE level (kU/L) comment
0 < ABSENT OR UNDETECTABLE ALLERGEN SPECIFIC IgE
1 LOW LEVEL OF ALLERGEN SPECIFIC IgE
2 MODERATE LEVEL OF ALLERGEN SPECIFIC IgE
3 HIGH LEVEL OF ALLERGEN SPECIFIC IgE
4 VERY HIGH LEVEL OF ALLERGEN SPECIFIC IgE
5 ULTRA HIGH LEVEL OF ALLERGEN SPECIFIC IgE
6 > EXTREMELY HIGH LEVEL OF ALLERGEN SPECIFIC IgE


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