Weekly issue 2026-W38 ·
Combining Cystatin C and Creatinine Increases eGFR Slope Accuracy in ADPKD
Plain language
Kidney function is usually estimated from one blood marker, creatinine. In 260 Dutch people with ADPKD, adding a second marker, cystatin C, tracked the true change in kidney function over time more closely than creatinine alone. That steadier signal could let future drug trials work with about a third fewer participants. For now it mainly matters for research, but it is a test you can ask your team about.
Clinical note
DIPAK observational cohort (n=260) with iothalamate mGFR. CKD-EPI 2021 eGFRcr (routine vs batch), eGFRcys and eGFRcr-cys compared. Cross-sectionally eGFRcr-cys most precise (more bias than eGFRcr). Longitudinally, eGFRcr-cys slope concordance with mGFR slope CCC 0.68 (0.59–0.76) vs 0.58 (0.47–0.67) for eGFRcr (P=0.02), with lower slope SD → 37–38% smaller trial sample sizes. Supports eGFRcr-cys as a trial end point; clinical use mainly where creatinine is unreliable.
Question for your next visit
Would measuring cystatin C as well as creatinine give a clearer picture of how my kidney function is changing?