A RAST test (short for radioallergosorbent test) is a blood test used to determine what a person 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.

A RAST test, using a person's extracted blood, detects the amount of IgE that reacts specifically with suspected or known allergens. IgE is the antibody associated with the allergic response: 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. It is worth noting that a person who has outgrown an allergy may still have a positive IgE years after exposure. Because there are other tests that help with confirmation, results are best interpreted by a doctor.

The RAST was introduced in the 1970's and replaced by a superior test in 1989. Advantages of the new test range from: improved sensitivity without loss of specificity, to excellent reproducibility across the full measuring range of the calibration curve. In general, this method of blood testing (in-vitro, out of body) vs skin-prick testing (in-vivo, in body) has many advantages: it is not always necessary to remove the patient from a medication regimen, skin conditions (such as eczema) don't affect results, it's less invasive (one venipuncture versus many skin pricks), and potentially dangerous substances are not introduced to a patient's body.

History

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The market-leading RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB, Uppsala, Sweden, and the acronymn 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.

External links

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• ImmunoCAP® articles, disease management data, product info:
  • http://www.immunocap.us
  • http://www.us.diagnostics.com
• Good general overview of RAST and skin-prick tests:
  • http://www.nyallergy.com/food_allergies.php#Diagnosis
• 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