After the RAST test

Following the withdrawal of blood, patients may resume medications and food intake according to their physician’s orders. Immediately after the blood sample is taken, the test tubes or paper are labeled with the date and the patient’s name, and they are sent to the laboratory for testing.

Results can be returned within days or several weeks, depending on which tests need to be performed. Based on the test results, additional blood tests may be ordered.

The meaning of the RAST results

Test results are always evaluated in relation to the “normal range” for that test. The range of values considered to be normal is the range of test results from the blood of normal, active healthy people.

When someone has a disease or health problem, the blood test results may be higher or lower than normal (“outside of the normal range”). When a physician sees that a blood test is outside of the normal range, a repeat test may be ordered to verify the results or additional tests may be required to determine the underlying causes behind the abnormality.

It is important to realize that RAST (or any other blood test) results are not absolute. Though positive results most probably indicate that the patient has a true allergy (an IgE response to that specific allergen), the results must always be interpreted by the specialist or physician. Results ultimately depend upon the individual's response in conjunction with specific symptoms and medical history. IgE levels may indicate an allergic reaction is taking place but if there are no physical symptoms being experienced, the individual does not have an allergy. If an individual's IgE test is negative, there is still a small possibility that the individual does have an allergy. In addition, the level of IgE present does not predict the potential severity of an allergic reaction in the patient.

Once an allergen is identified the offending substance should be avoided by the patient. Test results can easily be cross–checked by experience – if the offending substance is avoided and the patient gets healthier the procedure worked; if the patient does not get better it did not. A retest or another test or method may be needed to determine which allergen(s) are causing the symptoms to persist.  

When an allergy test pinpoints which allergen is causing an allergic reaction an allergist/immunologist will use the information to develop a treatment plan. The patient may be advised to make certain lifestyle modifications that may be effective in preventing symptoms on a day-to-day basis. Over-the-counter and/or prescription medications (e.g., antihistamines, decongestants) may also be recommended. Finally, if all other methods fail to treat the problem, allergy shots (immunotherapy) may be recommended.