DIRECT AND TOTAL BILIRUBIN TESTS - CONTEMPORARY PROBLEMS

In eight unique challenges mailed by The College of American Pathologi sts Comprehensive Chemistry Survey to participating laboratories withi n 3 years, results for direct-reacting bilirubin (DBIL) were highly va riable among the 12 largest peer groups, and most of the results diffe red greatly from the values obtained by a preferred method. Peer-group mean values for total bilirubin (TBIL) were in much better agreement with each other and with those obtained by the Reference Method for TB IL. From a review of the information on the assay of DBIL provided to us by the manufacturers, we conclude that among the major causes of th e large variability and bias in DBIL assays are problems with calibrat ion, lack of a serum blank measurement, inadequate concentrations of H CI in the reaction mixture, inappropriate use of bichromatic correctio n methods, and possibly the use of wetting agents or surfactants in th e reagent. Within-group SDs were small and generally acceptable. The a mong-peer-group variability in DBIL values is attributable to bias, no t imprecision. We recommend several simple changes that could improve the accuracy of DBIL determinations in clinical laboratories.