Is my Cystatin C normal?
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What is a normal Cystatin C level?
Cystatin C is a small protein produced at a constant rate by all nucleated cells and filtered exclusively by the kidneys. Its key advantage over creatinine: cystatin C is not affected by muscle mass, high-protein diets, or exercise — making it essential for accurate kidney assessment in bodybuilders, athletes, and anyone taking creatine supplements. Normal is 0.5-1.0 mg/L. Above 1.5 mg/L indicates significant kidney impairment. The 2021 CKD-EPI equation using cystatin C (or combined creatinine-cystatin C) provides the most accurate eGFR estimate and has been endorsed by the National Kidney Foundation as the preferred approach.
| Range | Values |
|---|---|
| Standard Reference | 0.5–1 mg/L |
| High Risk | > 1.5 mg/L |
What causes abnormal Cystatin C levels?
Elevated cystatin C is primarily caused by reduced kidney glomerular filtration rate (GFR) — meaning the kidneys are filtering blood less efficiently. Causes of reduced GFR include diabetes (diabetic nephropathy), hypertension (hypertensive nephropathy), chronic kidney disease, acute kidney injury, and nephrotoxic medications (NSAIDs, aminoglycosides). Unlike creatinine, cystatin C is minimally affected by muscle mass, making it reliable across all body types.
When should you see a doctor?
See your doctor if cystatin C is above 1.0 mg/L, especially if you have risk factors for kidney disease (diabetes, hypertension, family history). Above 1.5 mg/L warrants comprehensive nephrological evaluation. Cystatin C-based eGFR provides the most accurate staging of chronic kidney disease.
Cystatin C and longevity
Cystatin C has become the preferred kidney biomarker in longevity medicine because it eliminates the confounding variables that plague creatinine-based assessment. Athletic individuals often have elevated creatinine from high muscle mass, falsely suggesting kidney impairment. Conversely, sarcopenic elderly patients may have "normal" creatinine despite significantly reduced kidney function — a dangerous masking effect. The 2021 CKD-EPI cystatin C equation resolves these issues and also eliminates the race coefficient that was criticized for introducing health disparities. Beyond kidney function, elevated cystatin C independently predicts cardiovascular events and all-cause mortality in multiple large cohorts, suggesting it may capture broader aspects of vascular and inflammatory aging.
Where to get a Cystatin C test
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Related biomarkers
These biomarkers are often tested alongside Cystatin C for a more complete picture.
Frequently asked questions
What is a normal cystatin C level?
Is cystatin C better than creatinine?
When should I request cystatin C testing?
Is Cystatin C better than Creatinine for kidney function?
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Sources: Reference ranges based on AHA/ACC, ADA, and AACE clinical guidelines. Biological variation data from Ricos/Westgard database. Longevity-optimal ranges reflect targets used by preventive and functional medicine practitioners.
Last reviewed: April 2026. This tool provides general health information and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider about your specific results.