Allergy Skin Testing

What it is

Skin testing takes advantage of the fact that an allergic person carries antibodies to their allergen in the skin as well as the nose and lungs. A drop of extract is placed on the forearm or the back and the skin beneath is pricked or scratched so a trace of it gets past the surface. If the person is sensitized, that spot swells into a small itchy bump within about fifteen to twenty minutes, and the pattern of which spots react is the result. This code covers that percutaneous form of the test — prick, puncture or scratch. Injecting extract into the skin with a needle, and taping patches to the back for days to chase a contact rash, are different tests billed under different codes. A positive and a negative control are normally applied alongside the allergens, so the reader can tell a real reaction from skin that reacts to everything or to nothing.

Why it is done

• To identify what is behind persistent hay fever, year-round nasal congestion, or allergic eye symptoms
• To work out which triggers are contributing to asthma
• To investigate a suspected food allergy, alongside the history of what actually happened after eating
• To build the list an allergist needs before starting allergen immunotherapy

What to expect

Antihistamines blunt the reaction and have to be stopped for some days first — the allergist's office will say how long, and it varies by drug. The test itself takes a few minutes to apply and then a wait while the skin is watched. It stings briefly and the positive spots itch; that settles within an hour or so and a cream is often given. Because the extracts are being introduced into a sensitized person, a wider reaction is possible, which is why the testing is done in a supervised setting rather than at home. The allergist reads the pattern with the history in hand — a positive spot means sensitization, not automatically a clinically important allergy.

Questions worth asking

• How many allergens are planned for this session? This test is billed per allergen, so the count on the day drives the total more than anything else.
• Are the control tests counted among the billed items?
• If the prick tests come back negative and intradermal testing is done afterwards, is that a separate code and a separate charge on the same visit?
• Is the office visit billed in addition to the testing, and is the practice hospital-owned? An allergy clinic inside a hospital system can add a facility fee that a private office does not.