4 blood tests to detect allergies you should be aware of

By: Dr Varuna Mallya | | Updated: July 2, 2015 10:50 am

You must have seen many people avoid eating peanuts or seafood because they are allergic to them. These foods can trigger serious reactions like breathlessness or skin rashes and at times can also be fatal. However, getting treatment on time can easily avert all the complications.

1. Complete Blood Count (CBC): It is the most common blood test, and the doctor suggests it to see if you are suffering from an allergy. The test measures the number of specific white blood cells in the body called eosinophils that increases whenever the body encounters an allergen or foreign particles. Under normal conditions, the number of eosinophils is less than 8% of the total WBC count, but in case of allergy, the number increases. Along with CBC, the doctor will ask you to undergo an Absolute Eosinophil Count (AEC) that gives an exact number of eosinophils in the body. The normal range of eosinophils is 40-440 cells/ cu mm and a value exceeding the limit might indicate an allergy.

The reports of the test are available in around three hours and the CBC costs Rs 500, and AEC costs another Rs 300.

2. Enzyme Linked ImmunoSorbent Assay (ELISA) or EIA: ELISA is a blood test that measures the number of antibodies your body produces after encountering an antigen or a foreign particle. Antibodies are a part of your body’s immune system and can eliminate the antigen from your body. The results are available in a day, and the results are reported as negative, mild ( 1+), moderate ( 2+, 3+) or severe ( 4+, 5+). A value of 0- 40 is taken as negative, 80-150 as mild, 500-900 as moderate and more than 900 as severe with each value being in ng/ml. These tests are very expensive and cost between Rs 5000 to 25000. The test is done at specific centers and is extremely safe.

3. RadioAllergoSorbent Test (RAST): This test also detects antibodies to certain allergens but since it uses radioactive isotopes that are hazardous to health, it is not recommended anymore.

4. Skin test: The patient is asked to discontinue the use of anti-allergic medicines at least 48 hours before the test. An extract of the specific allergen is injected into your skin, and the response is noted. Allergen once it enters will stimulate the production of an antibody, this antibody will cause the release of substances in your body which will cause your skin to become red and itchy. For the test, you will have to give details about any medicines you are taking and this test is done in either of the following three ways:

a) Prick test or scratch test: It is done when you suspect an allergy but are not sure about the allergen. A drop of the allergen is put on your forearm or back after cleaning it with spirit. The skin surrounding it is then pricked mildly, and skin will be inspected for any redness or itch. Any redness ( erythema) or itchiness indicates that the test is positive and that you are allergic to that specific allergen.

b) Intradermal test: It is done when the prick test is inconclusive. A small quantity of the extract of allergen is injected into your forearm. It is inspected for any redness and swelling after 48 hours. A positive reaction indicates that your are positive for that allergen.

c) Patch test: The allergen extract is put on a patch and stuck on your forearm or back.

Prick test and patch test can be read in 15 to 20 minutes, and an Intradermal test is read after 48 hours. The patient is asked to avoid exposure to the allergen for which he is tested for at least 48 hours after the testing. Testing for each allergen costs around Rs 10,000.

Usually, there is no side effect of the test, but the doctor who does the test will keep all the emergency medicines in hand. Allergy testing is done at only specialized centers that deal with immunology.

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Published : July 1, 2015 7:55 am | Updated:July 2, 2015 10:50 am

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