Original Investigation
Pathogenesis and Treatment of Kidney Disease
Revised Equations for Estimated GFR From Serum Creatinine in Japan

https://doi.org/10.1053/j.ajkd.2008.12.034Get rights and content

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/1.73 m2 (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.

Section snippets

Inclusion and Exclusion Criteria

Inclusion criteria were: (1) age 18 years and older; (2) relatively stable kidney function, assessed by using SCr level; and (3) patient's agreement to have urinary Cin measured using a continuous infusion.

Exclusion criteria were: (1) acute kidney injury, (2) apparent malignancy, (3) problems in micturition, (4) pregnancy, (5) inulin allergy, (6) amputation, and (7) individuals for whom the investigator judged that measuring Cin was inappropriate. Although some study participants were

Patient Characteristics in the Development and Validation Populations

Characteristics of the development population (n = 413) and validation population (n = 350) are listed in Table 1. Distributions of participant numbers by cause of kidney disease and mean age, SCr level, albumin level, SUN level, height, weight, and body surface area were similar between the 2 populations. Mean Cin was also similar between them at 59.1 ± 35.4 mL/min/1.73 m2 in the development population and 57.2 ± 34.7 mL/min/1.73 m2 in the validation population. Proportions of participants

Discussion

We previously reported that eGFR calculated using either the IDMS–MDRD Study equation modified by using the JSN–CKDI coefficient (0.741; equation 1) or the JSN–CKDI equation (equation 2) was more accurate than the unmodified MDRD Study equation in Japanese individuals.19 The present study verifies our previous results, and accuracy of GFR estimation is improved further by means of newly derived equations, the modified IDMS–MDRD Study equation with the new Japanese coefficient (0.808; 95% CI,

Acknowledgements

Author affiliations are as follows. Department of Nephrology, Nagoya University Graduate School of Medicine, Nagoya, Japan: Seiichi Matsuo, MD, PhD, Yoshinari Yasuda, MD, PhD; Department of Nephrology, Osaka University Graduate School of Medicine, Suita, Japan: Enyu Imai, MD, PhD; Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Suita, Japan: Masaru Horio, MD, PhD; Department of Nephrology, Kumamoto University, Graduate School of Medicine, Kumamoto,

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    Originally published online as doi:10.1053/j.ajkd.2008.12.034 on April 2, 2009.

    A list of author affiliations appears at the end of this article.

    A list of the investigators who helped develop the Japanese equation for estimated GFR appears at the end of the article.

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