Kidney biomarker tool
Cystatin C eGFR Calculator for Adults
Estimate GFR from cystatin C, age, and sex with the CKD-EPI 2012 cystatin C equation, then review when a combined estimate may be more appropriate.
This is an educational estimate for adults with stable kidney function. Discuss results and the most appropriate equation with a healthcare professional.
How this tool works
This calculator implements the CKD-EPI 2012 cystatin C-only equation. It standardizes cystatin C against 0.8 mg/L, applies different exponents above and below that value, and adjusts for age and the sex term used in the published equation.
Cystatin C is less dependent on muscle mass than creatinine, but it is not unaffected by non-kidney factors. Inflammation, thyroid status, corticosteroid use, smoking, obesity, and the laboratory assay can influence a result. Clinicians often prefer the 2021 combined creatinine-cystatin C equation when both markers are available.
How to use it
- Use a cystatin C result in mg/L from a recent laboratory report and enter the age at the time of testing.
- Choose the sex term used by the published equation, then calculate the indexed result in mL/min/1.73 m².
- Compare the estimate with the laboratory report and any creatinine-based or combined estimate rather than interpreting it alone.
How to interpret the result
The number is an estimate of filtration normalized to a standard body surface area. CKD G categories use the same numerical ranges, but a category is not a diagnosis unless duration and other kidney-damage evidence are considered.
A meaningful difference between creatinine and cystatin C estimates can be clinically useful. It is a reason to review body composition, medicines, illness, assay quality, and whether a combined equation or measured GFR is needed; it is not proof that one marker is automatically correct.
Limitations and safety
- For adults with stable kidney function; it is not validated for a rapidly changing creatinine/cystatin C state or for children.
- Do not use the result alone to diagnose CKD, adjust a prescription, approve contrast, or make a transplant decision.
- Use the laboratory's reported result and a qualified clinician when precision affects care.
Sources and method
Formula and interpretation checked against the following primary or authoritative sources. Editorial review date: September 9, 2026.