Assessment of interference by aspirin with some assays commonly done in the clinical laboratory

We have assessed the interference of acetylsalicylic acid (aspirin) with some common clinical laboratory assays, because of its widespread use and reported interference. The therapeutic regimens involved ingestion of 10 325-mg tablets daily for three days or eight tablets for five days or two weeks. Twenty-one commonly done determinations were run on control sera, and sera were collected during and after drug therapy. Significant changes in t-test values, indicating the significance of the standard deviation of the difference between controls and specimens drawn after drug therapy, were observed for chloride (increased), and for total protein, calcium, cholesterol, uric acid, bilirubin, and thyroxine (decreased). Aspirin therapy depressed the apparent concentrations of these constituents progressively in the three-day regimen and initially in the long-term regimens, followed by recovery toward zero t-values at the end of the longer regimens.