Because patients may receive care at multiple locations within a geographic area, serum creatinine measurements must be standardized across laboratories to enable comparisons of reported estimated glomerular filtration rate (eGFR). The results of a successful creatinine standardization program designed to minimize the contribution of laboratory error to the reporting of eGFR are reported; 107 laboratories, which tested creatinine on 124 analyzers from six different manufacturers, voluntarily participated. Each laboratory received a correction factor to apply to its creatinine measurements to standardize them to the isotope dilution mass spectrometry reference method. The adjusted values were then used to calculate eGFR using the Modification of Diet in Renal Disease (MDRD) equation. The standardization program reduced the average total error in the measurement of creatinine from 23.9 to 8.7% and the average analytical bias from 16.5 to 2.7%. Implementing this program on a larger scale could reduce the rate of incorrect classification of stage 3 chronic kidney disease by 84%.