Testing for Allergy.
Allergy Test is carried out to determine the cause of allergy. These allergy tests are carried out by two methods:
1. Skin Test for allergy.
2. Blood Test for allergy.
3. Food Challenges Test.
Test for Allergy.
1. Skin Test for Allergy:
The allergy skin test is preferred over the allergy blood test because it is easier to carry out, and less expensive. This test also gives more specific information to detect the antigen responsible for causing the allergy. Results are also available much faster. This test is called the prick method test or the puncture method test.
Skin test for allergy is useful for diagnosing sources of
- Food Allergy,
- Allergy due to mold, pollen, animal dander,
- Drugs such as penicillin,
- Sources of contact dermatitis.
Procedure of Allergy Skin Test:
The skin of the forearm or the back is scratched with a needle whose tip has been soaked in the suspected antigens or their extracts. Various such scratches are made with the various antigens that normally cause allergy. These have been mentioned in “Allergy”.
Alternatively, the antigens or their extracts are injected separately into the dermis of the skin using a needle and a syringe.
These spots are then marked using a ink, making sure that the patient is not allergic to the ink itself.
Result of Allergy Skin Test.
These spots are then observed after 30 minutes. A positive reaction will show a formation of a wheal of redness. These reactions will vary in intensity are graded from 1+ to 4+. The more severe reactions can be in the form of a Hive, which has been explained “here”.
Photo of Allergy Skin Test result on back
Photo of Allergy Skin Test being done on forearm
2. Blood Test for Allergy.
This blood test, which is referred to as the RAST test for allergy or the radioallergosorbent test, is performed in vitro. ie. in the lab and not in vivo (in the body). About 5 ml blood is drawn from your body, and allergy blood test result takes about a week.
Indications for Allergy Blood Test.
- When you refuse to get pricked so many times, as required by the skin test,
- If you are required to be on anti allergic therapy.
- Widespread skin disease is present.
Principle of Allergy Blood Test.
The principle of this test is measuring of the absolute eosinophil count and IgE antibodies in the blood when the antigen has been added to the blood. We all have IgE antibodies in the blood, but higher levels of these antibodies indicate that you are sensitive to that antigen.
Disadvantages of Allergy Blood Test:
- Expensive.
- Result takes a week as compared to the skin test which takes 30 minutes.
- Doubtful accuracy with some antigens.
3) Food Allergy Test.
This food allergy test or the food challenges test, as the name suggests is done to find the food allergen that may have caused allergy. The patient is administered a capsule or pill containing the suspected allergen and he or she is watched for any reaction. This test is performed under supervision for fear of a severe allergic reaction, preferably in a hospital. By trial and error method, an effort is made to find the source of allergy, with the help of this food allergy testing.
However, you yourself, can play a vital role in identifying the substance that has caused an allergy, by being vigilant of what you eat or come in contact with, which triggers off this reaction.
Allergy testing has its drawbacks, in the sense that, it may give false positive or a false negative test report. It may show you as sensitive to a particular substance while the allergy may not be due to that substance.
Your action step.
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