Cystatin C | National Kidney Foundation https://www.youtube.com/watch?v=7-GXKDEYZOI Jul 26, 2023A past test for kidney function did not give clear results about your kidneys, so your healthcare provider wants to check again with a cystatin C test to be sure. You are older or have lots of muscle (such as a bodybuilder), where creatinine levels can vary. In these cases, a cystatin C test may.Sodium…