The importance of metrological traceability on the validity of creatinine measurement as an index of renal function.

The glomerular filtration rate (GFR) is currently considered the best overall index of kidney function. The possibility that laboratories might routinely report an estimated GFR has become practically feasible with the development of a formula, the "four-variable" Modification of Diet in Renal Disease study (MDRD) equation that uses age, sex, race, and serum creatinine parameters. However, a limitation of this equation for general implementation in healthcare is related to the use of differently calibrated creatinine measurement procedures among laboratories. The only way to achieve universal implementation of the GFR prediction equation, with the associated clinical benefits for patients, is, therefore, to promote worldwide standardization of methods to determine creatinine, together with the introduction of a revised GFR-estimating equation appropriate for use with standardized creatinine methods.