How many scratch tests

April 17, 2003

Availability of allergy extracts for testing can be compared to grocery shopping.

All grocery stores will offer milk, bread, eggs, canned goods, etc. But each store will also maintain it's own inventory which may or may not include your favorite brand or specialty item.

Laboratories that manufacture and supply allergy extracts are much the same. Most all of them will carry some variation of the pollens, molds, and environmentals common to most areas, but each lab may have items of their own unique inventory as well.

In addition, each physician will choose his own inventory of extracts from those available. Most physicians will select the most common allergens in his area to test for.

For example, pellitory is a European weed that many people are allergic to. While European physicians will test to pellitory, it's unlikely that American physicians will test to that weed, since it does not grow in the U.S.

On a smaller scale, California will have some of the same allergens as Arkansas, but they will have some different ones also. Each region will have it's own unique set of allergens.

The number of extracts a physician selects to have available for testing will vary according to the amount of allergens in his area, special needs in his community, recommendations from other sources or physician preference.

Some physicians select a certain number of extracts and test everyone to each of these most common allergens for their locale. Sometimes a doctor will selectively test for only a few allergens from her standard extracts, basing her choice on the patient's history.

For example if a patient reports that the only problem she experiences is when she is working in a damp basement, the physician may select to test only to molds.

If the patient says he is fine year round except for a few months in the summer, the physician may select to test for grasses and other pollens which are prevalent in his area during the months in which the patient experiences problems.

However, many physicians will probably test everyone to their standard inventory of extracts most of the time. In addition to those included in this standard testing tray, some physicians will have additional extracts available that can supplement their standard testing when indicated.

Many physicians also test for food allergies using the scratch test. Foods are not considered to cause the runny nose and itchy watery eyes usually associated with allergies. For this reason, foods are usually not tested unless there are specific symptoms that may relate to food allergy.

When I test a patient, I tell them, "We are testing you to the most common pollens, molds, and environmentals in this area." When they do not show allergy to the items we test them for, I never tell them "You are not allergic to anything." I do tell them, "You are not allergic to the most common allergens in our area."

I occasionally have people tell me they want to be tested to "everything." I remind them that there are so many substances in the world that it would be impossible to test to "everything." But I also reassure them that we are testing to the things that have been found to be the most likely to cause allergy symptoms in our area.

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