RAST test
Encyclopedia
A RAST test is a blood test used to determine to what substances a person is allergic
. This is different from a skin allergy test
, which determines allergy by the reaction of a person's skin to different substances.
Because there are other tests that help with confirmation, results are best interpreted by a doctor.
, Uppsala, Sweden, and the acronym RAST is actually a brand name. In 1989, Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which literature may also describe as: CAP RAST, CAP FEIA (fluorenzymeimmunoassay), and Pharmacia CAP. 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 0-100, is the only specific IgE assay to receive FDA approval to quantitatively report to its detection limit of 0.1kU/l. This clearance is based on the CLSI/NCCLS-17A Limits of Detection and Limits of Quantitation, October 2004 guideline.
The guidelines for diagnosis and management of food allergy issues by the National Institute of Health state that:
"sIgE levels were originally measured using the radioallergosorbent test (RAST), but this test has been replaced by more sensitive fluorescence enzyme-labeled assays and the term RAST should be abandoned"
Advantages of the allergy blood test range from: excellent reproducibility across the full measuring range of the calibration curve, it has very 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 anthihistamine 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.
Adults and children of any age can take an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin tests.
In the NIH food guidelines issued in December 2010 it was stated that “The predictive values associated with clinical evidence of allergy for ImmunoCAP cannot be applied to to other test methods.” With over 4000 scientific articles using ImmunoCAP and showing its clinical value, ImmunoCAP is perceived as “Gold standard” for in vitro IgE testing
antibodies to suspected or known allergen
s. 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 have 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 amount of radioactivity is proportional to the serum IgE for the allergen.
RAST are often used to test for allergies when:
• a physician advises against the discontinuation of medications that can interfere with test results or cause medical complications
;
• a patient suffers from severe skin conditions such as widespread eczema
or psoriasis
; or
• a patient has such a high sensitivity level to suspected allergens that any administration of those allergens might result in potentially serious side effects.
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
. This is different from a skin allergy test
Skin allergy test
Skin allergy testing is a method for medical diagnosis of allergies that attempts to provoke a small, controlled, allergic response. -Process:A microscopic amount of an allergen is introduced to a patient's skin by various means:...
, which determines allergy by the reaction of a person's skin to different substances.
Because there are other tests that help with confirmation, results are best interpreted by a doctor.
History
The market-leading RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics ABPharmacia
Pharmacia was a pharmaceutical and biotechnological company in Sweden.-History:Pharmacia was founded in 1911 in Stockholm, Sweden by pharmacist Gustav Felix Grönfeldt at the Elgen Pharmacy. The company is named after the Greek word φαρμακεία, transliterated pharmakeia, which means 'sorcery'...
, Uppsala, Sweden, and the acronym RAST is actually a brand name. In 1989, Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which literature may also describe as: CAP RAST, CAP FEIA (fluorenzymeimmunoassay), and Pharmacia CAP. 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 0-100, is the only specific IgE assay to receive FDA approval to quantitatively report to its detection limit of 0.1kU/l. This clearance is based on the CLSI/NCCLS-17A Limits of Detection and Limits of Quantitation, October 2004 guideline.
The guidelines for diagnosis and management of food allergy issues by the National Institute of Health state that:
"sIgE levels were originally measured using the radioallergosorbent test (RAST), but this test has been replaced by more sensitive fluorescence enzyme-labeled assays and the term RAST should be abandoned"
Indication
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 have similar diagnostic value in terms of sensitivity and specificity.Advantages of the allergy blood test range from: excellent reproducibility across the full measuring range of the calibration curve, it has very 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 anthihistamine medication regimen, and if the skin conditions (such as eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
) 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.
Adults and children of any age can take an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin tests.
In the NIH food guidelines issued in December 2010 it was stated that “The predictive values associated with clinical evidence of allergy for ImmunoCAP cannot be applied to to other test methods.” With over 4000 scientific articles using ImmunoCAP and showing its clinical value, ImmunoCAP is perceived as “Gold standard” for in vitro IgE testing
Method
The RAST test is a radioimmunoassay test to detect specific IgEImmunoglobulin E
Immunoglobulin E is a class of antibody that has been found only in mammals. IgE is a monomeric antibody with 4 Ig-like domains...
antibodies to suspected or known allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
s. IgE is the antibody
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
associated with Type I allergic response
Type I hypersensitivity
Type I hypersensitivity is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen, or to a nonimmunologic stimulus like cold weather or exercise...
: for example, if a person exhibits a high level of IgE directed against pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
, the test may indicate the person is allergic to pollen (or pollen-like) proteins. A person who has outgrown an allergy may still have 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 amount of radioactivity is proportional to the serum IgE for the allergen.
RAST are often used to test for allergies when:
• a physician advises against the discontinuation of medications that can interfere with test results or cause medical complications
Complication (medicine)
Complication, in medicine, is an unfavorable evolution of a disease, a health condition or a medical treatment. The disease can become worse in its severity or show a higher number of signs, symptoms or new pathological changes, become widespread throughout the body or affect other organ systems. A...
;
• a patient suffers from severe skin conditions such as widespread eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
or psoriasis
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...
; or
• a patient has such a high sensitivity level to suspected allergens that any administration of those allergens might result in potentially serious side effects.
Scale
The RAST test is scored on a scale from 0 to 6:| RAST rating | IgE level (KU/L) | comment |
|---|---|---|
| 0 | < 0.35 | ABSENT OR UNDETECTABLE ALLERGEN SPECIFIC IgE |
| 1 | 0.35 - 0.69 | LOW LEVEL OF ALLERGEN SPECIFIC IgE |
| 2 | 0.70 - 3.49 | MODERATE LEVEL OF ALLERGEN SPECIFIC IgE |
| 3 | 3.50 - 17.49 | HIGH LEVEL OF ALLERGEN SPECIFIC IgE |
| 4 | 17.50 - 49.99 | VERY HIGH LEVEL OF ALLERGEN SPECIFIC IgE |
| 5 | 50.0 - 100.00 | VERY HIGH LEVEL OF ALLERGEN SPECIFIC IgE |
| 6 | > 100.00 | EXTREMELY HIGH LEVEL OF ALLERGEN SPECIFIC IgE |
External links
- A discussion by world renowned experts on the relative value of RAST testing from the American Academy of Allergy, Asthma and Immunology (AAAAI), the largest professional medical specialty organization representing allergists, clinical immunologists, allied health professionals, and other physicians with a special interest in allergy
- http://www.aaaai.org/aadmc/ate/category.asp?cat=1137
- ImmunoCAP articles, disease management data, product info from the manufacturer that markets this product:
- http://isitallergy.com/
- http://www.phadia.us/
- Short FAQ's: How a RAST test is performed, results, when ordered:
- http://www.healthatoz.com/healthatoz/Atoz/dc/tp/tprast.jsp
- http://www.labtestsonline.org/understanding/analytes/allergy/test.html
- A glossary of allergy testing information regarding RAST
- http://www.acaai.org/public/background/testing.htm