Every parent of an allergic child is anxious to find out all the things in the world that the child is allergic to. That's why allergy testing is one of the most common requests parents make of their pediatricians. Before jumping the gun and ordering a bunch of tests, parents must understand how these tests are used and interpreted. Misinterpreting the results can actually do more harm than good.
The Skin Scratch Test
To figure out the potential for various food allergies, the skin prick test is one of the most common methods of determining sources of allergy. One of the advantages of performing skin tests is that the result is immediately available. The test can be quickly performed in the doctor's office, and it is not necessary to get any blood drawn at a lab.
To conduct this test, the doctor scratches the skin lightly with a needle and then places a small amount of purified allergen extract onto the scratched skin surface. If the child has an allergy to the item under scrutiny, the skin swells up and becomes red and itchy.
Your doctor should explain to you that prior to undergoing skin allergy testing, your child must refrain from using any oral antihistamines for at least one day. The test must be performed under the supervision of a physician who can handle an emergency in case a severe allergic reaction results from the scratch test. Most importantly, the skin test results must be interpreted by an experienced allergy expert. Misinterpreting the results can have a detrimental effect on your child. Most pediatricians prefer consulting an allergy specialist for such an evaluation.
When should my child be tested for food allergies?
Skin testing may be warranted if a severe allergic reaction has occurred and your doctor strongly suspects that food is the culprit. Indiscriminant testing without considering an individual's clinical history can only result in misdiagnosis and unnecessary dietary restrictions.
The Blood Test
While skin allergy testing is considered superior and more reliable than allergy testing through the blood, the advantage of a blood test is that the result is generally easier to interpret. Any experienced pediatrician can order and interpret the result of allergy blood tests without consulting an allergy specialist. Another advantage of performing the blood test is that patients do not have to stop taking antihistamines before the test is performed. Oral antihistamines (or any other medications, for that matter) do not influence the result of allergy blood tests. Finally, there is no risk for the child of a severe anaphylactic reaction when this test is performed.
There are some inherent limitations of blood allergy testing. People may test positive for certain types of food when they in fact do not have allergy to those food items. This false-positive result would lead them to avoid these foods unnecessarily. The results of blood allergy testing also take a lot longer to come back, compared to the immediacy of skin testing.
Misinterpretation of Results
No matter what type of allergy testing is desired, it is essential that the test results be interpreted correctly. Most general pediatricians and family practice physicians do not have the expertise or clinical experience to properly interpret the results of skin allergy tests. Misinterpreted results may remove many foods unnecessarily from your child's menu. More seriously, incorrect interpretation could lead to a false sense of security and expose your child to potential dangerous sources of food allergy.
There is a common misconception that toddlers and infants are too young to be candidates for allergy testing. Even though infants younger than twelve months might have a less intense skin reaction to the allergen challenge, a skin allergy test can still be reliably performed and interpreted. It is usually performed under the supervision of an allergy specialist.
On the other hand, many general physicians are supremely qualified to evaluate the results of blood tests for food allergy. Politely ask your doctor about his experience with other children with food allergy. Your doctor will probably refer your child to an allergy expert if he does not feel comfortable interpreting these results himself.