RAST test
| radioallergosorbent test | |
|---|---|
| Medical diagnostics | |
| MeSH | D011852 |
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 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. Since at least 2010, health organizations in the US have recommended that the RAST be abandoned as a diagnostic test for allergy in favor of more sensitive fluorescence enzyme-labeled assays.
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) 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. However, skin testing techniques have improved. Most skin testing does not involve needles and typically skin testing results in minimal patient discomfort.
Drawback to RAST and ImmunoCAP techniques do exist. Compared to skin testing, ImmunoCAP and other RAST techniques take longer to perform and are less cost effective. Several studies have also found these tests to be less sensitive than skin testing for the detection of clinically relevant allergies. False positive results may be obtained due to cross-reactivity of homologous proteins or by cross-reactive carbohydrate determinants (CCDs).
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