Clinical Decisionmaking

Reactivity to allergen skin tests has no bearing on mortality or cancer risk

Allergies affect at least 10 percent of the population and 75 percent of those whose parents both have allergies, and the incidence of allergies is increasing worldwide. It has long been speculated that atopy—or reactivity to allergen skin testing—has a broader influence on health than just the allergic symptoms associated with it. Some think that it may boost or weaken immune system surveillance. For example, atopy may play a protective role in cardiovascular disease by increased immune system activity resulting in decreased platelet aggregation (blood thickness) or increase risk via mast cell release of histamine provoking coronary artery spasm. Another theory is that atopy may speed up cancer via an excessively active immune system which attacks the body's own cells, or it may prevent cancer by keeping aberrant cells in check.

Conflicting findings of previous studies are due in part to methodological issues and failure to control for important cancer and cardiovascular risk factors such as smoking. However, a recent study that controls for such factors shows no relationship between atopy and subsequent mortality.

Peter J. Gergen, M.D., of the Agency for Healthcare Research and Quality, and his colleagues used data from the second National Health and Nutrition Examination Survey (NHANES II), a representative sample of the U.S. population from 1976-1980, to compare baseline health status and atopic status (allergen skin test reactivity) with cause of death through 1992 for participants 30 years of age or older at baseline. Reactivity was defined as a weal (a raised bump on the skin) 3 mm or larger in response to one of eight allergens ranging from house dust and cat to ragweed and Bermuda grass.

The investigators found no association between allergen skin test reactivity and deaths from all causes. Results did not change when cancer or heart disease mortality was examined separately. Likewise, the presence or absence of allergic symptoms did not alter findings.

More details are in "Is allergen skin test reactivity a predictor of mortality? Findings from a national cohort," by Dr. Gergen, Paul C. Turkeltaub, M.D., and C.T. Sempos, Ph.D., in Clinical and Experimental Allergy 30, pp. 1717-1723, 2000.

Reprints (AHRQ Publication No. 01-R062) are available from the AHRQ Publications Clearinghouse.

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