Cystatin C Plus Creatinine Improves Estimation of GFR

An equation adding data on cystatin C to serum creatinine improves accuracy in estimating GFR, reports an article in the New England Journal of Medicine.

The Chronic Kidney Disease Epidemiology Collaboration study included data on more than 5352 individuals enrolled in 13 studies. The researchers developed equations for estimating GFR based on cystatin C alone and cystatin C plus standardized creatinine. The equations were validated in a set of 1119 participants from five studies who had undergone GFR measurement.

Compared with equations using either creatinine or cystatin C, the combined equation provided better performance in estimating GFR. Although bias was similar between the three equations, precision was higher with the combined cystatin C–creatinine equation. The interquartile range of the difference between estimated and measured GFR was 13.4 mL/min/1.73 m2 with the combined equation, compared with 15.4 mL/min/1.73 m2 with the creatinine equation and 16.4 mL/min/1.73 m2 with the cystatin C equation.

The combined equation also offered increased accuracy and improved classification of chronic kidney disease (CKD). Among participants with a creatinine-based estimated GFR of 45–74 mL/min/1.73 m2, the net reclassification index for the presence of CKD (60 mL/min/1.73 m2) was 19.4 percent. Among those with an estimated GFR of 45–59 mL/min/1.73 m2, the combined equations correctly reclassified 16.9 percent of participants as not having CKD.

The combined equation based on standardized creatinine and cystatin C offers better performance in estimating GFR, and it may also improve the classification of patients with CKD. The researchers write, “The new equations represent an advance over currently available equations across the range of GFR and in relevant subgroups.” [Inker LA, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med 2012; 367:20–29].

September 2012 (Vol. 4, Number 9)​