Integer Cystatin C Values: Impact on Discordance Group Assignment and Accuracy of GFR-Estimating Equations

What is it about?

Doctors need a measure to know how well your kidneys are working. Two tests, one measuring a substance called creatinine and the other cystatin C, are commonly used for this. Fu and colleagues previously said combining these two tests gives a better picture of kidney health than either test alone. But, they represented cystatin C values in whole numbers, which might not be as precise. We ran a similar study to theirs with data from 698 people, and especially looked at a group of people whose tests suggest they might have more muscle mass. We noticed that if we also reported cystatin C values as whole numbers, it changed both the number of people falling into this group and how accurate our measurements were. We found that the less precise we were with cystatin C values, the bigger the changes. This could mean that the initial findings by Fu and colleagues require careful interpretation.

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