Cystatin C Doesn’t Beat Creatinine in Estimating GFR

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Estimates of glomerular filtration rate (GFR) based on cystatin C are not significantly better than estimates based on plasma creatinine, according to a study in Kidney International.

The iohexol clearance method was used to measure GFR in a general population sample of 1621 middle-aged adults, all free of coronary heart disease, kidney disease, stroke, or diabetes. Published equations for estimating GFR based on cystatin C or plasma creatinine measurements were compared in terms of bias and precision, calculated as the median and interquartile range of estimated minus measured GFR, respectively. Accuracy was expressed as the percentage of estimates

Estimates of glomerular filtration rate (GFR) based on cystatin C are not significantly better than estimates based on plasma creatinine, according to a study in Kidney International.

The iohexol clearance method was used to measure GFR in a general population sample of 1621 middle-aged adults, all free of coronary heart disease, kidney disease, stroke, or diabetes. Published equations for estimating GFR based on cystatin C or plasma creatinine measurements were compared in terms of bias and precision, calculated as the median and interquartile range of estimated minus measured GFR, respectively. Accuracy was expressed as the percentage of estimates within 30 percent of measured GFR.

The best-performing equation based on cystatin C had an accuracy of 94 percent, with bias of 3.5 and precision of 18 mL/min/1.73 m2. By comparison, one creatinine-based equation offered accuracy of 95 percent, with bias of 2.9 and precision of 7.6 mL/min/1.73 m2. An equation incorporating both measurements offered accuracy of 92 percent, with bias of 7.6 and precision of 15 mL/min/1.73 m2. None of the equations based on cystatin C—alone or in combination with creatinine—provided a better estimate of GFR than the widely used Modification of Diet in Renal Disease and Chronic Kidney Disease Epidemiology Collaboration equations.

Estimates based on cystatin C are superior to creatinine in predicting cardiovascular disease. It has been suggested that cystatin C-based equations might be superior to creatinine-based equations in predicting GFR values near the range of normal.

However, this study finds that cystatin C-based equations are not superior to creatinine-based equations in predicting GFR in a healthy middle-aged population. The cardiovascular predictive value of cystatin C may involve factors other than GFR, the authors suggest [Eriksen BO, et al. Cystatin C is not a better estimator of GFR than plasma creatinine in the general population. Kidney Int 2010; 78: 1305–1311].

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