Combined Creatinine–Cystatin C eGFR — CKD-EPI 2021
The combined CKD-EPI 2021 equation uses serum creatinine, cystatin C, age and sex. Cystatin C is less dependent on muscle mass but has non-GFR determinants, including glucocorticoids, thyroid disease and inflammation.
When to use it
Use to confirm CKD staging in patients with atypical muscle mass (amputees, the frail elderly, body-builders) or when an accurate GFR is needed before nephrotoxic therapy. KDIGO suggests combining creatinine and cystatin C for greatest accuracy.
Formula
eGFRcr-cys = 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=0.7/0.9 and α=−0.219/−0.144 for female/male. Creatinine in mg/dL, cystatin C in mg/L.
Category
Kidney Function
References
- Inker LA et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385:1737-1749. PMID: 34554658
About NephroMind
This calculator is part of NephroMind, a free clinical decision-aid platform from the Arab Society of Nephrology and Renal Transplantation (ASNRT) — over 128 bedside nephrology calculators plus a renal drug-dosing database, coded by a practicing transplant nephrologist.