Use of a synthetic soluble bilirubin derivative to assess interference in creatinine measurements.

In assessing interference from bilirubin, the use of a synthetic soluble derivative (ditaurobilirubin, DTB) is recommended as a surrogate for the natural conjugates (Bc). We compared the interference effect of unconjugated bilirubin (Bu), Bc, and DTB, using six mechanized methods for serum creatinine measurement. No significant interference was noted in methods that include removal of proteins or in an enzymatic method involving NADH oxidation. Heavy (negative) interference was observed in an alkaline picrate method, and in direct enzymatic methods based on hydrogen peroxide measurement: interference was always more pronounced in the presence of the two soluble derivatives (Bc and DTB), whose interference was of the same magnitude. These results point out the utility of testing for bilirubin interference by using soluble derivatives, in addition to Bu, and suggest the feasibility of using DTB as a surrogate for Bc for this purpose.