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—Dr Levy makes a valid point that drug therapy can sometimes produce abnormalities on laboratory test results. We did not collect specific data on drug therapy for each patient during this study, but more than 90% of our population was taking at least one drug, and most patients were taking two or more. Thus, it is certainly possible that some of the abnormal results could have been due to drug effects. In fact, we did indicate that some of the abnormalities (eg, electrolyte disturbances and azotemia) were related to drug therapy for chronic conditions.The main thrust of our article was, however, to determine the benefit of routine annual laboratory tests in a nursing home population, not simply to discover the incidence of abnormal results. Dr Levy's point about drug interference, while important in interpreting abnormal test results in individual patients, does not change the validity or the
Mark R. Levinstein, Joseph G. Ouslander, Laurence Z. Rubenstein. Drug Use and Laboratory Values in the Elderly-Reply. JAMA. 1988;259(6):841–842. doi:10.1001/jama.1988.03720060013017