Multicentre physiological reference values for the concentration of creatininium in plasma and diagnostic specificity of glomerular filtration rate estimated with the MDRD equation.

BACKGROUND: The National Kidney Disease Education Program recommends that clinical laboratories, when asked for an estimation of glomerular filtration rate in a patient by means of the "four-variable" Modification of Diet in Renal Disease (MDRD) Study equation, also provide the measurement result for creatininium concentration in plasma and the appropriate reference interval. On the other hand, clinical laboratories seeking accreditation for compliance with ISO 15189:2003 need to demonstrate that the physiological reference intervals communicated to all users of laboratory services are appropriate for the patient population served, and for their measurement systems. METHODS: Ten clinical laboratories in different regions of Spain collaborated in identifying reference individuals and producing reference values for the concentration of creatininium in plasma using RD/Hitachi Modular Analytics analysers, and for the volume rate of glomerular filtrate in kidneys (glomerular filtration rate), estimated with the "four-variable" MDRD Study equation. All the logistic work was carried out in co-operation with the supplier of the reagents and analysers (Roche Diagnostics Espa?a, S.L., Sant Cugat del Vallès, Catalonia, Spain). Using all the reference values obtained by each laboratory, multicentre reference limits were estimated non-parametrically. RESULTS AND CONCLUSIONS: Reference intervals estimated in this study for concentrations of plasma creatininium are 52-85 micromol/L for women and 64-106 micromol/L for men. The diagnostic specificity of the estimated glomerular filtration rate is 99.2% when applied to healthy persons to screen for chronic kidney disease.