Cystatin C

•Observational— More accurate than creatinine in muscular or low-muscle adults

Why it matters beyond creatinine

Creatinine is produced from muscle — muscular athletes overestimate GFR, frail elderly underestimate it. Cystatin C is produced by all nucleated cells at a more constant rate, so its eGFR doesn’t depend on muscle mass.

Independent prognostic value

Beyond kidney function, cystatin C predicts cardiovascular events and all-cause mortality independently of creatinine-based eGFR — partly because it captures inflammation and frailty signals not in creatinine alone.

Combined equation (best)

The CKD-EPI 2021 equation using both creatinine and cystatin C provides the most accurate eGFR. Many panels now report it as eGFR-cr-cys.

Cost and availability

Cystatin C is moderately more expensive than creatinine but widely available in major labs. Use when:

• Creatinine eGFR is borderline and decision-relevant.
• Drug dose adjustment matters (chemotherapy, anti-arrhythmics).
• The patient has unusual body composition.
• Long-term risk stratification.

Related entries

eGFR, Chronic kidney disease, Frailty.