A study of interferences in routine methods for creatinine measurement.

A survey was undertaken through the Irish External Quality Assessment Scheme to investigate the extent to which acetoacetate and bilirubin affect routine methods in current use for measurement of serum creatinine. Spiking a sample with 10 mmol/l acetoacetate caused errors ranging from -28% to +22%. The greatest errors were found with end-point Jaffé methods and kinetic Jaffé methods in which there was no time delay between final reagent addition and start of absorbance measurement. A sample with high bilirubin concentration gave apparent creatinine results ranging from zero to 280 mumol/l. Although these interferences are well documented in the literature, this knowledge seems to have had little effect on methods in actual use.