Allergy testing negative, symptoms real

September 24, 2003

The most important allergy test, according to many physicians, is called the History and Physical (H&P). If I have rhinitis, watery eyes, or an asthma attack every time I am exposed to a substance, and the physical exam is consistent with a diagnosis of allergies, it is likely I am allergic to that substance. Sinus pressure, ear pressure, and hoarseness can also be related to allergy.

The other side of the coin is that what I label as my allergy symptoms may really be symptoms of something unrelated to allergies. Your physician will likely correlate that H&P with allergy and other testing to determine what is the underlying cause of your symptoms.

Allergy testing can help pinpoint exactly what substance is causing allergy symptoms, but allergy testing is not 100% accurate. However, for the most part, I've found allergy testing to be remarkably reliable. I've tested thousands people for allergies over the years, and many have been helped by immunotherapy to substances for which we found them to be allergic.

When patients have symptoms in spite of negative allergy testing, it is likely they are experiencing something that mimics allergies, such as non-allergic rhinitis (see footnote). However, it is also possible to be allergic to a substance, yet have a false negative allergy test.

For skin testing, it is very important to leave off antihistamines and some other medications such as certain antidepressants prior to testing. Taking these medications during the days preceding skin testing may cause the test to be negative. Never leave off antidepressant medication without your physician's approval, though. For more information, see:
Antihistamines: Preparing for allergy testing and
Antidepressants: Preparing for allergy testing

Repeating negative allergy tests at a later date and possibly by a different method may be helpful. However, we've found that repeat skin testing a few months or years later continues to be negative for most whose original tests were negative.

Usually by the time the physician has finished the H&P, she has a pretty good idea of how the allergy testing will turn out. For example, when a patient always experiences hay fever in the fall, it is likely ragweed or other fall pollens are the culprit. The physician will look for physical symptoms of allergies, such as pale, boggy nasal mucosa.

Yet there remains that occasional patient whose allergy testing is negative in spite of a positive H&P.

Often treating the symptoms with medications such as antihistamines will help. Sometimes a CT Scan (Cat Scan) of the sinuses reveals chronic sinusitis or nasal polyps or other sinus abnormalities. The physician I work for often orders a sinus CT in conjunction with allergy testing, because often both sinus abnormalities and allergies can be contributing to the problem. When allergy testing is negative, it is especially important to consider other possibilities such as sinus abnormalities. Sometimes surgical intervention is required.

The physician does not focus on one specific test, but correlates symptoms, physical findings, health history, test results, and environmental conditions to determine the most likely diagnosis and best treatment plan for each patient.

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