Interpretation
| Result | Meaning |
|---|---|
| ≥ 90 | G1 |
| 60–89 | G2 |
| 45–59 | G3a |
| 30–44 | G3b |
| 15–29 | G4 |
| < 15 | G5 |
Formula
eGFR = 135 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−0.544 × min(Scys/0.8, 1)^−0.323 × max(Scys/0.8, 1)^−0.778 × 0.9961^age × 0.963 [if female]; κ = 0.7 (F) / 0.9 (M); α = −0.219 (F) / −0.144 (M). Scr in mg/dL, Scys in mg/L.
Clinical pearls
- Cystatin C is less affected by muscle mass and diet, but is raised by high-dose corticosteroids, thyroid dysfunction, inflammation and obesity.
- Use when creatinine eGFR is unreliable (sarcopenia, amputation, very high muscle mass, vegetarian diet) or to confirm CKD G3a when no albuminuria is present.
- Cystatin C assays must be calibrated to the IFCC reference material (ERM-DA471) for this equation.
Examples
egfr with cystatin c 1.4 and creatinine 1.3, 72 year old womanckd-epi cr-cys 60M cr 110 umol/L cys c 1.2combined egfr creat 1.0 cystatin 1.0 age 50 male
FAQ
When should cystatin C be used to estimate GFR?
When creatinine-based eGFR may be inaccurate (abnormal muscle mass or diet) or a more accurate value matters for diagnosis or drug dosing; KDIGO recommends the combined creatinine–cystatin C equation.
Is the cystatin C eGFR more accurate than creatinine alone?
Yes. In the 2021 CKD-EPI validation the combined equation had the smallest bias and the highest proportion of estimates within 30% of measured GFR.