Renal function
Cystatin C
Low-molecular-weight protein freely filtered; GFR estimator independent of muscle mass.
Sample
Serum
Clinical reference range
0.5 to 1 mg/L
Adult
Conv: 0.5–1 mg/L
Biology
What it measures
Produced at constant rate by all nucleated cells; freely filtered then catabolized by proximal tubule (not secreted). Less affected by muscle mass, diet, and race.
Clinical use
Why we order it
Confirm CKD when creatinine is misleading (low muscle mass, amputees, athletes); refine drug dosing.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Combined eGFR (creatinine + cystatin C) is the most accurate non-isotopic estimate.
Differential
Causes of abnormal values
Causes of HIGH
- ↑GFR decline
- ↑Hyperthyroidism
- ↑High-dose steroids
- ↑Active inflammation/cancer (less than creatinine but real)
Related