Title: GFR Estimation Using Standardized Serum Cystatin C in Japan
Abstract: <h3>Background</h3> Recently, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) developed glomerular filtration rate (GFR)-estimating equations based on standardized serum cystatin C (CKD-EPI<sub>cys</sub>) and standardized serum creatinine plus standardized serum cystatin C (CKD-EPI<sub>cr-cys</sub>). We developed new GFR-estimating equations based on standardized cystatin C for a Japanese population and compared their accuracy with the CKD-EPI equations. <h3>Study Design</h3> Accuracy of diagnostic test study. <h3>Setting & Participants</h3> 413 (development data set) and 350 individuals (validation data set). <h3>Index Test</h3> CKD-EPI<sub>cys</sub>; CKD-EPI<sub>cr-cys</sub>; modifications to CKD-EPI<sub>cys</sub> and CKD-EPI<sub>cr-cys</sub> using Japanese coefficients; and newly developed Japanese eGFR equations based on standardized serum cystatin C (Eq<sub>cys</sub>), cystatin C with a nonrenal factor reflecting hypothesized extrarenal elimination (Eq<sub>cys+nonrenal</sub>), and creatinine in combination with cystatin C (Eq<sub>cr-cys</sub>). Standardized cystatin C values were determined by a colloidal gold immunoassay traceable to the international certified reference material ERM-DA471/IFCC. <h3>Reference Test</h3> Measured GFR by inulin renal clearance. <h3>Results</h3> In a development data set, we calculated Japanese coefficients for CKD-EPI<sub>cys</sub> and CKD-EPI<sub>cr-cys</sub> of 0.977 (95% CI, 0.853-1.002) and 0.908 (95% CI, 0.889-0.928), respectively. In a validation data set, we compared CKD-EPI<sub>cys</sub>, Eq<sub>cys</sub>, and Eq<sub>cys+nonrenal</sub> with each other. Bias and accuracy were not significantly different among the 3 equations. The precision of CKD-EPI<sub>cys</sub> was significantly better than for Eq<sub>cys</sub> (<i>P</i> = 0.007) and not significantly different from Eq<sub>cys+nonrenal</sub> (<i>P</i> = 0.6). We then compared 0.908 × CKD-EPI<sub>cr-cys</sub>, Eq<sub>cr-cys</sub>, and Eq<sub>average</sub> (the average value of Eq<sub>cr</sub> [previous Japanese equation based on standardized serum creatinine] and Eq<sub>cys+nonrenal</sub>) with each other in the validation data set. Bias and accuracy were not significantly different among the 3 equations. The precision of 0.908 × CKD-EPI<sub>cr-cys</sub> was significantly better than for Eq<sub>cr-cys</sub> (<i>P</i> = 0.004) and not significantly different from Eq<sub>average</sub> (<i>P</i> = 0.06). <h3>Limitations</h3> Limited number of participants with measured GFR >90 mL/min/1.73 m<sup>2</sup>. Extrarenal elimination of cystatin C was not measured. <h3>Conclusions</h3> CKD-EPI<sub>cys</sub> performed well in Japanese individuals, suggesting that equations based on serum cystatin C could be used in patients with different races without modification. Accounting for extrarenal elimination of cystatin C may improve the performance of estimating equations.
Publication Year: 2012
Publication Date: 2012-08-11
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 248
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