GFR estimation using self-directed 24-hour urine collection for creatinine clearance is less accurate than using the CKD-EPI equation. A larger study is required to clarify GFR in healthy Asians, and the association of health outcomes of Asian kidney donors with lower GFR thresholds.

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INTRODUCTIONThe use of coefficients to adjust for ethnicity in equations estimating glomerular filtration rate (GFR) is impractical. (1,2) Although coefficients for ethnicities other than 'white' or 'black' have been derived for the Modification of Diet in Renal Disease (MDRD) equation, these coefficients do not necessarily yield accurate estimations.(1,3) The combined use of serum creatinine and cystatin C biomarkers in equations estimating GFR has been shown to improve the accuracy of GFR estimation and reduce the effect of ethnicity as a predictor.(4) In fact, a recent study showed that the effect ethnicity had on GFR estimation was rendered insignificant when beta-trace protein (BTP), creatinine and cystatin C were used in the equation. (5) The equation developed by the Chronic Kidney DiseaseEpidemiology Collaborative Group (CKD-EPI) is preferred when estimating GFRs in multiethnic populations because of its reduced bias. CKD-EPI has also developed a new equation that incorporates both serum creatinine and cystatin C, using a population comprising both healthy individuals and chronic kidney disease (CKD) patients.(2) We assessed the performance of the new creatinine-cystatin C CKD-EPI equation in a study cohort consisting of healthy participants and patients with CKD who have undergone radionuclide GFR measurement. METHODSThe present study, which was approved by the institution review board, utilised the serum samples of research participants (n = 335) from the Asian Kidney Disease Study and Singapore Kidney Function Study. (3,6) The stored serum samples were assayed for cystatin C. In the Asian Kidney Disease Study, patients with stable CKD from the outpatient renal clinics of National University Hospital, Singapore, were recruited (n = 232).(3) In the Singapore Kidney Function Study, healthy participants who had normal kidney function and who reported having no diagnosis of hypertension or diabetes mellitus were recruited (n = 103). (6) All participants from both studies underwent urine dipstick tests to exclude microalbuminuria, leucocyturia and erythrocyturia. Participants were recruited consecutively using stratified sampling; they were stratified according to the four ethnic groups (Chinese, Malay, Indian and others) and then by gender. In both studies, participants performed self-directed 24-hour urine collections and underwent GFR measurements the next day, during which blood and spot urine samples were also collected.