Background: Estimation of glomerular filtration rate (GFR) is limited by differences in creatinine generation among ethnicities. Our previously reported GFR-estimating equations for Japanese had limitations because all participants had a GFR less than 90 mL/min/1.73 m2 and serum creatinine was assayed in different laboratories. Study Design: Diagnostic test study using a prospective cross-sectional design. New equations were developed in 413 participants and validated in 350 participants. All samples were assayed in a central laboratory. Setting & Participants: Hospitalized Japanese patients in 80 medical centers. Patients had not participated in the previous study. Reference Test: Measured GFR (mGFR) computed from inulin clearance. Index Test: Estimated GFR (eGFR) by using the modified isotope dilution mass spectrometry (IDMS)-traceable 4-variable Modification of Diet in Renal Disease (MDRD) Study equation using the previous Japanese Society of Nephrology Chronic Kidney Disease Initiative (JSN-CKDI) coefficient of 0.741 (equation 1), the previous JSN-CKDI equation (equation 2), and new equations derived in the development data set: modified MDRD Study using a new Japanese coefficient (equation 3), and a 3-variable Japanese equation (equation 4). Measurements: Performance of equations was assessed by means of bias (eGFR-mGFR), accuracy (percentage of estimates within 15% or 30% of mGFR), root mean squared error, and correlation coefficient. Results: In the development data set, the new Japanese coefficient was 0.808 (95% confidence interval, 0.728 to 0.829) for the IDMS-MDRD Study equation (equation 3), and the 3-variable Japanese equation (equation 4) was eGFR (mL/min/1.73 m2) = 194 × Serum creatinine-1.094 × Age-0.287 × 0.739 (if female). In the validation data set, bias was -1.3 ± 19.4 versus -5.9 ± 19.0 mL/min/1.73 m2 (P = 0.002), and accuracy within 30% of mGFR was 73% versus 72% (P = 0.6) for equation 3 versus equation 1 and-2.1±19.0 versus-7.9±18.7 mL/min/1.73m2 (P<0.001) and 75% versus 73% (P= 0.06) for equation 4 versus equation 2 (P = 0.06), respectively. Limitation: Most study participants had chronic kidney disease, and some may have had changing GFRs. Conclusion: The new Japanese coefficient for the modified IDMS-MDRD Study equation and the new Japanese equation are more accurate for the Japanese population than the previously reported equations. Am J Kidney Dis 53:982-992.
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