Interference with clinical laboratory analyses.

Interference by endogenous and exogenous substances with assays for clinical analytes is a common problem in laboratory medicine. For this review, we defined interference as "the effect of a substance present in the sample that alters the correct value of the result, usually expressed as concentration or activity, for an analyte." There are four major endogenous compounds that consistently interfere with laboratory results: hemoglobin, bilirubin, lipids, and paraproteins. The major exogenous sources of interference are drugs prescribed for the patient; and there are several excellent compendia of the effect of drugs on clinical laboratory tests. We recommend determining whether the interference is dependent or independent of the analyte for the assay. Further, we propose an approach to the identification and resolution of an interference problem for the clinical laboratory and make recommendations to manufacturers.