Skin tests for allergic disorders have been around since the 1860s. Today, prick or puncture tests are commonly used by allergists as diagnostic aids. These tests are not very invasive and, for most allergens, they tend to produce quick results. If the results of prick or puncture tests are negative, they may be followed by intradermal tests, which give allergists more details about what’s causing the underlying symptoms.
Here is how both types of tests are administered:
- Prick/puncture. A diluted allergen is applied with a prick or a puncture on the surface of the skin.
- Intradermal. Using a 26- to 30-guage (very thin) needle, a diluted allergen is injected immediately below the skin surface.
After either type of test, the area of the skin is observed for about 15 minutes to see if a reaction develops. The “wheal”—a raised, red, itchy bump and surrounding “flare”—indicates the presence of the allergy antibody when the person is exposed to specific allergens. The larger the wheal and flare, the greater the sensitivity.
Although skin testing may seem simple, it must be carried out by trained practitioners with an understanding of the variables and risks of the testing procedure.
Steps should include:
- After reviewing the patient’s medical history and performing a physical exam, the allergist determines that allergy skin testing is both appropriate for the patient and does not put the patient at risk for a bad outcome (such as severe anaphylaxis or an asthma attack in poorly controlled asthma).
- A trained nurse performs the skin testing under the supervision of the allergist.
- The allergist personally “reads” the skin tests and, in evaluating the skin test reactions, discerns several factors that lead to proper interpretation.
These factors include:
- Proper evaluation and selection of which patient may benefit from skin testing
- Condition and reactivity of the skin
- Proper selection of where the skin tests are placed
- Type of skin test placed
- Device used for skin testing
- Proper technique in applying the tests
- Quality and selection of the allergen extracts used
- Medications that could alter the validity of the results
In addition to carefully considering allergy testing variables, board-certified allergists are trained to report test results according to standard practices endorsed by the American College of Allergy, Asthma & Immunology.
Standardized allergy test records are vital since patients often change doctors. When they do, their new allergist must be able to accurately interpret their health records. If information is incomplete, patients may be ordered to undergo additional skin testing that would have been unnecessary had standard practices been followed.
Guidelines suggest that skin test records report the diameter of the wheal and the surrounding “flare” (measured in millimeters) and record information to account for the differences in testing devices. The measurements are usually reported in millimeters of diameter.
Allergy nurses performing allergy and asthma tests are also required to meet basic quality assurance standards to ensure that they are using the proper techniques.
Seeing a board-certified allergist will assure these guidelines are followed. Allergy skin testing is relatively safe; adverse reactions are rare. Even so, researchers recommend that the value of any test be carefully considered before it is administered.