Skin tests, first developed almost a century ago, are still the mainstay of allergy testing. They are easy and safe to do, give fast results, and are relatively inexpensive, which makes them the best way to start looking for specific allergies.
In performing scratch skin tests, drops of allergen extracts (eg, pollens, dust mites, molds, animal danders, foods) are allowed to seep through shallow scratches made in the patient’s skin. The tests can also be performed by the deeper, intradermal technique, in which extracts are injected under the skin. There are pros and cons to both testing methods. Scratch tests are painless and very easy to do. They are somewhat less sensitive than intradermal tests; they are also less likely to cause a severe reaction in someone who is highly allergic. The intradermal tests, which let the allergen extracts penetrate deeper into the skin, are highlysensitive, but they can occasionally result in false-positive reactions, indicating allergies where none exist. Your physician may decide to start with scratch tests, then go on to intradermal testing if further information is needed. Before testing, your doctor will ask you not to give your child any antihistamines for 3 to 5 days, as they will interfere with the results of the tests.
If your child has formed specific IgE antibodies through earlier exposure to one of the substances being tested, the skin test area will redden and swell into a disk that looks like a mosquito bite around the puncture site. This skin reaction usually peaks within 15 to 20 minutes after the test extracts are applied, and then gradually clears up. The skin where the tests were done may feel itchy for a few hours.
Skin Tests Must Be Done by an Experienced Physician
Although a positive result to scratch or intradermal skin testing strongly suggests that your child has formed lgE antibodies against a specific allergen, it does not follow that your child will definitely develop allergy symptoms when exposed to that particular allergen in the environment. As a rule, the bigger the skin test reaction, the higher the chances are that your child is allergic and will sneeze, itch, or break out in a rash. However, in some cases the skin reaction is trivial while the symptoms are overwhelming, and vice versa. Further, even though your child may have diminished symptoms as he gets older, the skin test result can remain positive. It is important that tests be conducted and results interpreted by someone trained and experienced in allergy skin testing.
This Is Only a Test
Many parents and children are afraid of having allergy skin testing because they’ve heard false reports that it is painful and upsetting. Scratch tests, the form of testing most often used in children, are mostly painless because they are done on the surface of the skin, where there aren’t any nerve endings to register pain. Furthermore, new test devices are available that can do up to 8 tests at a time and allow scratch testing to be done quickly and without injury. The intradermal technique uses a very fine needle to penetrate the surface of the skin. It is “felt” a little more than scratch testing but is still not very painful.
Many people also falsely believe that children have to reach a certain age before they can be tested. In fact, age is no barrier to skin testing; positive results can be obtained at any age. For example, in infants and toddlers who have eczema and suspected food allergy, skin tests often reveal sensitivity to milk or egg. Once parents have this information, they can keep those foods out of their child’s diet to control allergy symptoms.
Finally, experienced doctors and nurses perform allergy testing on a daily basis. They know how to take away fears and put children—and parents—at ease.