Diagnostics: Allergy Testing

Allergy testing looks for signs that the immune system has become sensitized to substances such as pollens, molds, dust mites, and animal dander.

What Allergy Testing Is

Allergy testing looks for signs that the immune system has become sensitized to specific substances in the environment, called allergens. Common allergens include tree, grass, and weed pollens; indoor and outdoor molds; dust mites; and cat, dog, rodent, or cockroach material.

When a person is sensitized, the body makes an antibody called immunoglobulin E (IgE) that is directed against a particular allergen. Allergy tests detect this IgE, either by watching the skin react to a tiny amount of allergen or by measuring allergen-specific IgE in a blood sample.

A positive test shows sensitization, not necessarily a true allergy. Many people have positive tests without any symptoms. Results only become meaningful when a clinician interprets them alongside the person's symptoms, history, and exposures.

Why It Is Used in Ear, Nose, and Throat Care

Allergies can drive or worsen several conditions that ear, nose, and throat clinicians and allergists evaluate:

• Allergic rhinitis (hay fever): sneezing, runny or stuffy nose, and itchy, watery eyes triggered by allergens. Testing helps clarify whether symptoms are allergic and which allergens are responsible. See nose and sinus conditions.

• Chronic rhinosinusitis: long-lasting inflammation of the nose and sinuses. Allergies can be a contributing or aggravating factor in some people, and testing is one option for identifying allergic triggers. See sinus infection.

• Eustachian tube dysfunction: the tube connecting the middle ear to the back of the nose can become blocked or work poorly when allergic inflammation affects the surrounding tissues, leading to ear fullness, pressure, or muffled hearing. See Eustachian tube dysfunction.

Identifying relevant allergens can inform treatment options such as allergen avoidance, medications, or allergen immunotherapy (allergy shots or under-the-tongue treatment). Related information is available on the nose and sinus treatments page.

Skin Prick Testing

Skin prick testing (also called a scratch or puncture test) is usually the first-choice skin test. Small drops of different allergen extracts are placed on the skin of the forearm or back, and the skin is lightly pricked or scratched through each drop so a tiny amount enters the surface layer.

If a person is sensitized, a small raised, red, itchy bump (a "wheal and flare" reaction) develops at that spot within about 15 to 20 minutes. Each test includes a positive control (usually histamine) and a negative control to help interpret the results. Many allergens can be tested in one session, and results are available during the same visit.

Intradermal Testing

Intradermal (also called intracutaneous) testing involves injecting a small amount of diluted allergen just beneath the surface of the skin, usually on the forearm, using a very thin needle. As with prick testing, the site is watched for a wheal and flare reaction over the following 10 to 15 minutes.

This test is more sensitive but less specific than prick testing, meaning it can detect weaker sensitivities but also produces more false-positive results. It is generally used only when the prick test is negative but suspicion of a particular allergy remains high. An allergen that already tested positive on prick testing is not retested this way. Intradermal testing also carries a somewhat higher chance of a stronger reaction than prick testing.

Blood (Serum Specific IgE) Testing

This test measures the amount of IgE directed against specific allergens in a blood sample sent to a laboratory. It does not require pricking or injecting the skin, and results take longer than skin testing because the sample must be processed.

Blood testing is especially useful when skin testing is not practical, for example when a person has widespread skin disease such as eczema, has skin that reacts to any scratch, cannot safely stop antihistamines, or has had a severe allergic reaction in the past. An older name for this test, "RAST," has been replaced by more sensitive modern assays.

What to Expect

Testing is usually done in a clinic by an allergist or another trained clinician. Skin testing may cause temporary itching, redness, and small bumps at reactive sites that typically settle within a few hours. Blood testing involves a standard blood draw. For children, numbing cream may be applied to the skin before skin testing. A clinician equipped to treat allergic reactions supervises skin testing.

How Results Are Interpreted

• A positive result means sensitization (the presence of IgE to that allergen), not an automatic diagnosis of allergy. Confirming an allergy requires that the positive result match real-world symptoms on exposure.

• Larger skin reactions or higher blood IgE levels generally indicate a greater likelihood of true clinical allergy, but they do not reliably predict how severe symptoms will be.

• Test results do not always agree with one another, because skin tests measure IgE bound to skin cells while blood tests measure IgE in the bloodstream.

• Broad, undirected panels are discouraged. Testing many allergens without regard to a person's history and local environment often turns up irrelevant positives that can lead to unnecessary avoidance.

Limitations

• Both false-positive and false-negative results occur.

• Sensitization is common in people without symptoms, so tests must be interpreted in clinical context.

• Cross-reactivity between similar proteins can cause positive results that are not clinically important.

• Results from different laboratories or testing systems are not always directly comparable.

• Tests for allergen-specific IgG antibodies are not useful for diagnosing allergies.

Medication Considerations

Certain medicines can blunt skin test reactions and cause falsely negative results, so they are often paused for a period before skin testing. Blood testing is not affected by these medicines.

• Antihistamines (oral and topical nasal or eye forms) are the most common cause of false-negative skin tests. Depending on the specific drug, they are typically held for several days up to about one to three weeks before testing, according to the testing clinician's instructions.

• Tricyclic antidepressants and certain other medicines with antihistamine effects are usually held for about a week.

• Topical steroids applied to the test site may need to be paused beforehand.

• Short courses of oral steroids generally do not interfere with skin test results.

Decisions about pausing any medicine are made with the prescribing or testing clinician.

Risks

Skin testing is generally safe. The most common effects are temporary itching, redness, and swelling at test sites. Serious, whole-body allergic reactions are rare but possible, which is why testing is done where trained staff and emergency treatment are available. The risk of a stronger reaction is somewhat higher with intradermal testing than with prick testing. People taking beta-blocker medicines may react more strongly and may respond less well to the usual emergency treatment, so this is typically discussed beforehand. Blood testing carries only the minor risks of a routine blood draw, such as bruising.

The Bottom Line

Allergy testing is a tool for pinpointing the allergens behind nasal, sinus, and ear symptoms, but no test stands alone. Results are most useful when a clinician combines them with a careful history and examination.