A new equation that uses both creatinine and cystatin C measurements provides a more accurate estimate of kidney function than either marker alone, according to a new study that included data from diverse populations totaling 5,352 participants across 13 studies.

The equation may be useful as a confirmatory test for CKD. Among subjects with an estimated glomerular filtrate rate (eGFR) of 45 to 74 mL/min/1.73m2 based on creatinine alone, the combined equation improved the classification of measured GFR as either less than 60 or 60 or greater (net reclassification index, 19.4%), and correctly reclassified 16.9% of those with eGFR of 45 to 59 as having a GFR of at least 60, according to findings published in the New England Journal of Medicine (2012;367:20-29).

In a statement released by the National Institutes of Health, which funded the study, lead investigator Lesley Inker, MD, a nephrologist at Tufts Medical Center in Boston, observed: “The new creatinine-cystatin equation is more accurate over a broader range of kidney function and body size, and less altered by other medical conditions.”

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