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Use of Cystatin C to Assess Kidney Function



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Slide 25

August 2011

Now let us go back to our patient we started off the presentation discussing. As you recall, he is a 66-year-old African American gentleman with a serum creatinine of 1.5 mg/dL. His MDRD estimated GFR comes out to 57 mL per minute per 1.73 m2. Using the CKD-EPI equation we get a very similar number of 55 mL per minute per 1.73 m2. Therefore he clearly has stage 3 chronic kidney disease, and is potentially at risk for further loss of kidney function.

At this point, it would be extremely helpful to further understand his risk, especially since this was 1 of his key questions. Two tests that are extremely helpful to address this question are the urine albumin creatinine ratio and a serum cystatin C. In the table on this slide, I have used the data from the 2 large studies previously discussed in order to roughly estimate what his risk of end-stage renal disease would be based upon hypothetical results of the these 2 additional tests. The urine albumin creatinine ratio could either be normal at 20 mg per gram, or slightly high at 100 mg per gram. Similarly his cystatin C could either be normal at 1.1 mg/L which equates to an estimated GFR of 68 mL per minute per 1.73 m2 or it could be slightly elevated at 1.4 mg/L to give an estimated GFR of 47 ml/min/1.73m2. If he had normal cystatin C and normal albumin creatinine ratio his risk of end-stage renal failure is 4 times higher than persons without an elevated creatinine at all. However, if his cystatin C is also high this risk increases to 31 times above baseline. Furthermore, if cystatin C and albumin creatinine ratio are both high his risk increases to over 400 times baseline values. These calculations provide an idea how use of cystatin C could help us to identify patients at particularly high risk of future renal failure and cardiac vascular events.

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