An abnormal laboratory value in any patient must be explained. Three factors may alter the laboratory test results: diet, disease, and drugs. Perusal of the Physicians' Desk Reference reveals the enormous influence drugs can have on the laboratory test results. The prescribing physician should be aware of any potential side effects of a drug he or she is prescribing and enlist the assistance of a qualified pathologist to decide what effects, if any, the medication has on observed anomalies. The clinical pathologist can also help the clinician to decide what further steps need to be taken to elucidate the problem.