Estimates of GFR (eGFR) based on cystatin C—alone or combined with creatinine—improve the prediction of adverse clinical outcomes related to kidney function, according to a meta-analysis in the New England Journal of Medicine.
The meta-analysis included data from 11 general population studies, with nearly 91,000 participants, and five cohort studies including nearly 3000 patients with chronic kidney disease. All reports provided information on standardized serum creatinine and cystatin C measurements. The eGFRs based on cystatin C, creatinine, or both were evaluated for associations with mortality, death of cardiovascular disease, or ESRD.
In the general population studies, the prevalence of eGFR less than 60 mL/min/1.73 m2 was higher with estimates based on cystatin C than in those based on creatinine: 13.7 percent versus 9.7 percent. For all three outcomes, risk was decreased when eGFR was reclassified to a higher value based on cystatin C, and it was increased when eGFR was reclassified to a lower value based on creatinine.
Cystatin-based eGFR was associated with a net reclassification improvement of 0.23 for death and 0.10 for ESRD. This was so with estimates based on either cystatin C alone or cystatin C plus creatinine. With both methods, mortality was significantly increased below a threshold eGFR value of about 85 mL/min/1.73 m2.
Using cystatin C to calculate eGFR increases the accuracy of kidney function estimates. The new results suggest that cystatin C–based estimates strengthen the association between eGFR and adverse outcomes, especially all-cause mortality, but also cardiovascular mortality and ESRD. The study “provides evidence that the use of cystatin C improves the role of eGFR in risk categorization” [Shlipak MG, et al. Cystatin C versus creatinine in determining risk based on kidney function. N Engl J Med 2013; 369:932–943].
