Skip to content
Blood Test Tracker

eGFR calculator from creatinine and cystatin C (CKD-EPI 2021)

An estimate of how well your kidneys filter blood, worked out from both your creatinine and cystatin C levels plus your age and sex. Type your results in the units on your report and it works out eGFR (cr-cys) as you type, in your browser.

AI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-03Kidneys

mg/L
In years, on the day of the blood test.
years
The equation has a version for each.

Type your results above, or fill in the example, to see eGFR (cr-cys).

Nothing you type here leaves your browser.

Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.

How it’s worked out

The formula

eGFR (mL/min/1.73 m²) = 135 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−0.544 × min(Scys/0.8, 1)^−0.323 × max(Scys/0.8, 1)^−0.778 × 0.9961^age × 0.963 [if female]; Scr = serum creatinine in mg/dL, Scys = serum cystatin C in mg/L, age in years; κ = 0.7 (female) or 0.9 (male); α = −0.219 (female) or −0.144 (male)

When the equation works

Outside these limits the calculator says so instead of giving a number.

  • Creatinine: 0.2 to 15 mg/dL
  • Cystatin C: 0.3 to 8 mg/L
  • Age: 18 years and over

A worked example

Example numbers, not anyone’s real results, run through the same code as the calculator above.

Example inputs and the result
Creatinine1 mg/dL
Cystatin C1 mg/L
Age60 years
SexFemale
eGFR (cr-cys)71 mL/min/1.73 m²

For a woman aged 60, this result is in the usual range.

What eGFR (cr-cys) tells you

eGFR stands for estimated glomerular filtration rate, a measure of how much blood your kidneys filter each minute. This version uses two blood markers, creatinine and cystatin C, along with your age and sex. Creatinine depends partly on muscle mass and diet, and cystatin C is affected by different things, so using both usually gives a more accurate estimate than either one alone. Many labs now use the 2021 CKD-EPI equation, which does not use race.

KDIGO 2024 recommends this combined estimate when a creatinine-only eGFR is likely to be less accurate and the result will affect decisions, such as staging chronic kidney disease or drug dosing. It also says that if cystatin C is available, the combined estimate should be used to place kidney function into stages. Like any eGFR, one value is not enough. Chronic kidney disease needs lower kidney function or other signs of kidney damage that last at least 3 months.

Read the full page on eGFR (cr-cys), with what a high or low result can mean.

Usual ranges

The ranges the result above is placed on. Your own lab’s printed range comes first if it gives one.

Sources

The equation

  1. CKD-EPI Creatinine-Cystatin Equation (2021), National Kidney Foundation
  2. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race, New England Journal of Medicine (2021)
2 more sources for the ranges and the explanation
  1. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease, Kidney International 105(4S):S117-S314 (2024)
  2. Cystatin and Creatinine With eGFR (test 3018316), ARUP Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. The calculator is version 1.0.0 of our code for this equation, tested against published examples. How we build and check these pages.

More kidneys calculators

Every calculator