Nephrology

CKD-EPI Cystatin C eGFR Calculator

Calculates eGFR from serum cystatin C alone (adults)

Primary source: Inker LA et al. N Engl J Med 2012; 367: 20-29 (CKD-EPI cystatin C)

Aleksandr A. Aulov, MD, internal medicine Last clinical review: April 28, 2026

Online calculation

Serum cystatin C

mg/L

Age

years

Sex

About this score

CKD-EPI cystatin C (2012) estimates GFR from serum cystatin C. Cystatin C is a protein produced by all nucleated cells, freely filtered at the glomerulus, and largely independent of muscle mass, sex, and race, which makes it a more accurate marker of renal function than creatinine in a number of clinical situations.

It is used as a confirmatory calculation in patients with borderline creatinine-based eGFR, in patients with extreme muscle mass (bodybuilders, amputees, elderly patients with sarcopenia), in children, and in the assessment of renal transplant function. A combined CKD-EPI creatinine + cystatin C equation, which incorporates both markers, is considered the most accurate.

KDIGO 2024 guidance includes cystatin C as a recommended second marker for CKD staging in borderline cases. However, the assay costs more than creatinine, and availability may be limited to major centers and specialized laboratories in many settings.

When to use

Confirming CKD stage when creatinine-based eGFR is borderline (45–60 mL/min/1.73 m²) without markers of kidney damage.
Patients with extreme muscle mass (bodybuilders, amputees, severe sarcopenia).
Assessment of renal transplant function.
In children, where it is more accurate than creatinine-based equations.

Parameters in detail

Serum cystatin C

Serum cystatin C concentration, mg/L. Typical range roughly 0.5–2.5 mg/L.

Age

Patient age in years.

Sex

Biologic sex, used as a coefficient in the CKD-EPI cystatin C equation.

Clinical example

Case

A 75-year-old man with severe sarcopenia after prolonged immobilization. Creatinine 75 µmol/L, creatinine-based CKD-EPI eGFR ≈ 95 mL/min (appears normal). Cystatin C 1.8 mg/L.

Calculation

Using CKD-EPI cystatin C with a cystatin C of 1.8 in an elderly man, eGFR ≈ 38 mL/min/1.73 m².

Interpretation and management

The true eGFR is markedly lower than the creatinine-based estimate, a classic example of the creatinine blind spot in sarcopenia. The actual stage is G3b, not G1. Management: review drug dosing (especially NSAIDs, diuretics, metformin), check albuminuria, and consider nephrology referral. Serial cystatin C measurements can track the trend.

Limitations and cautions

The assay costs more than creatinine, limiting widespread use.
Availability may be limited to major centers and specialized laboratories in many settings.
Cystatin C can be elevated independent of renal function in active inflammation, high-dose glucocorticoid therapy, and hyperthyroidism.
Not validated in pregnancy.

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Frequently asked questions

When should creatinine be supplemented with cystatin C?

In diagnostic uncertainty (eGFR 45–60 without other markers of damage), in patients with extreme muscle mass, and when evaluating transplant candidates or transplant recipients.

What if creatinine- and cystatin C-based eGFR differ substantially?

Use the combined CKD-EPI creatinine + cystatin C equation, or direct measurement of clearance (inulin, iohexol). A discrepancy greater than 30% warrants further evaluation.

Is cystatin C valid in the elderly?

Yes, and it is often more accurate than creatinine in this group because of sarcopenia and reduced muscle mass.

Can it be used in patients on chemotherapy?

With caution. Some cytotoxic agents and glucocorticoids affect cystatin C independent of renal function. Interpret within the clinical context.

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Aleksandr A. Aulov Physician, internal medicine, Sechenov School — independent medical education platform. Calculators are compiled from the original publications and current clinical guidelines. Interpretation thresholds follow the source study unless stated otherwise.

This calculator is intended for healthcare professionals. Do not use it for self-diagnosis or self-treatment. Management decisions are made by the treating clinician based on the full clinical picture of the individual patient.