Many physicians refer to allergy-related blood tests that test immunoglobulin E (IgE) levels as a RAST but this may not be the exact testing method that the lab is using. There are other blood tests that may be used. For example, some tests will measure other substances in the blood, which may be more effective at pinpointing particular allergens.

Other types of blood tests include:

• CAP-RAST FEIA. This blood test is similar to RAST but is more useful in determining reactivity to certain foods.
  
  
• Radio allergo sorbent procedure (RASP). This blood test is a variant of the RAST but is more sensitive to food allergens. RASP may measure some immunoglobulin G (IgG) complexes in addition to IgE. However, the role of IgG complexes is not entirely clear and this test may not always provide valid results.
  
  
• Fluorescent allergo sorbent test (FAST). This blood test is similar to RAST but uses fluorescent instead of radioactive compounds to test the blood. This makes the equipment well-suited for use in an office (instead of a laboratory), where results can be delivered in about six hours.
  
  
• Multiple antigen simultaneous test (MAST). A spinoff of the RAST that proponents believe is more comprehensive and sensitive than its predecessor. MAST testing allows physicians to test for 38 allergens at a time (although it cannot diagnose food allergies), whereas RASTs look at only a single allergen per test.
  
  
• Immunoassay capture test. One of the newest blood tests. Proponents say the process used to make the patient’s blood and the test medium react leads to a result as sensitive and accurate as those obtained from allergy skin testing.
  
  
• Paper radioimmunosorbent test (PRIST). This test measures the total number of IgE antibodies in the blood.
  
  
• Complement testing. Complement is made up of proteins that bind with antibodies, and is involved in immune system functioning. Patients with hives or angioedema often show a deficiency in blood complement. Complement levels also can help a physician determine whether a case of angioedema is related to an allergy or to hereditary factors. This is important, because treatments differ for the two conditions.
  

  

Though the RAST and related blood tests can help diagnose an allergy, not all blood tests are reliable. Complementary and alternative medicine allergy tests (e.g., cytotoxic testing), for instance, do not provide reliable or useful diagnostic results.