The equation used by egfr() with method = "CKDEPI 2021 cystatin".
Details
The CKD-EPI 2021 creatinine-cystatin equation: $$eGFR = 135 \cdot \min(S_{cr}/\kappa, 1)^\alpha \cdot \max(S_{cr}/\kappa, 1)^{-0.544} \cdot \min(S_{cys}/0.8, 1)^{-0.323} \\ \cdot \max(S_{cys}/0.8, 1)^{-0.778} \cdot 0.9961^A \cdot 0.963^F$$
where:
\(S_{cr}\) = serum creatinine (mg/dL)
\(S_{cys}\) = serum cystatin C (mg/L)
\(\kappa\) = 0.7 (female) or 0.9 (male)
\(\alpha\) = -0.219 (female) or -0.144 (male)
\(A\) = age (years)
\(F\) = 1 (female) or 0 (male)