Cystatin C optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for Cystatin C:
- Optimal 0.6 – 1 mg/L (0.6 – 1 μg/mL); sufficient 0.5 – 1.2 mg/L (0.5 – 1.2 μg/mL); out of range above 1.2 mg/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mg/L | 0.6 – 1 | 0.5 – 1.2 | above 1.2 |
| μg/mL | 0.6 – 1 | 0.5 – 1.2 | above 1.2 |
Bounded on the high side only — a low result is not treated as out of range. No source gives a low cystatin C a clinical meaning, and 0.5 mg/L matches no published lower limit.
What the evidence says
KDIGO recommends it specifically to confirm a borderline creatinine-based eGFR before diagnosing chronic kidney disease, because creatinine reflects muscle mass and cystatin C does not. Raised independently by thyroid dysfunction, corticosteroids and obesity, so those have to be excluded before reading it as kidney function. The bands are a laboratory reference interval, not a guideline threshold: Mayo Clinic Laboratories reports up to 1.03 mg/L under age 50 and up to 1.21 mg/L from 50, which is where the optimal and acceptable bands end. A low result has no published meaning and is not flagged.
Sources
- CSTCE - Overview: Cystatin C with Estimated Glomerular Filtration Rate (eGFR), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceCystatin C reference values: 0.63 to 1.03 mg/L at ages 18 to 49, 0.67 to 1.21 mg/L at 50 and over. Sera's acceptable upper edge of 1.2 matches the older-adult limit; its optimal upper edge of 1.0 matches the under-50 limit.
What Cystatin C measures
A small protein filtered freely by the glomerulus, used as a measure of kidney function that does not depend on muscle mass.
The answer to creatinine's main weakness: creatinine reflects muscle, so it overstates kidney function in a frail or sarcopenic person and understates it in a muscular one. Cystatin C avoids that, and KDIGO recommends it to confirm a borderline eGFR before labelling someone with chronic kidney disease. It is raised independently by thyroid dysfunction, steroids and obesity.