eGFR Calculator (CKD-EPI 2021)

Calculate estimated GFR from serum creatinine using the CKD-EPI 2021 equation.

Serum creatinine (mg/dL) (mg/dL)

Age (years) (years)

Sex

Serum cystatin C (mg/L, optional) (mg/L)

0 = creatinine only

Please check your inputs and try again.

What Changed in the 2021 Equation

Earlier CKD-EPI and MDRD equations included a race coefficient that raised estimated GFR for Black patients by about 16%. The 2021 revision removed it entirely.

The rationale was that race is a social rather than biological category, and the coefficient could delay referral, transplant listing and specialist care by making kidney function appear better than it was. The refit equation uses only creatinine, age and sex.

Equation	Race coefficient	Status
MDRD	Yes	Superseded
CKD-EPI 2009	Yes	Superseded
CKD-EPI 2021	No	Current standard
CKD-EPI cystatin C	No	Confirmatory

Staging and Albuminuria

Stage	eGFR	Note
G1	≥ 90	Normal — needs albuminuria to diagnose CKD
G2	60–89	Mildly reduced — same caveat
G3a	45–59	Mild to moderate
G3b	30–44	Moderate to severe
G4	15–29	Severe — prepare for replacement
G5	< 15	Failure

A common error is diagnosing CKD from eGFR alone in stages G1 and G2. Those values are within the normal range, so kidney disease requires evidence of damage — usually albuminuria — alongside them. Albuminuria predicts outcomes independently of eGFR, which is why staging is reported as a grid of both.

When Creatinine Misleads

Creatinine derives from muscle, so eGFR is unreliable at extremes of body composition — amputees, bodybuilders, the severely cachectic. Cystatin C is produced by all nucleated cells and is largely independent of muscle mass, which is why it is recommended for confirmation when creatinine-based eGFR does not fit the clinical picture.

Note also that eGFR is normalised to 1.73 m² body surface area. That is right for staging but wrong for drug dosing, where the patient's actual clearance matters.

Worked Examples

Example 1: Female, 45yo, Cr=1.0mg/dL

CKD-EPI 2021 calculation

Result: eGFR≈75 mL/min/1.73m² (G2)

Mildly reduced — monitor over time

Example 2: Male, 70yo, Cr=1.8mg/dL

eGFR significantly reduced

Result: eGFR≈32 mL/min/1.73m² (G3b)

Drug dose adjustment needed; nephrology referral

Example 3: Why albuminuria matters

eGFR 75 with ACR 90 mg/g versus eGFR 75 with normal ACR

Result: CKD versus no CKD

Identical filtration, different diagnosis. Albuminuria supplies the evidence of damage that stages G1 and G2 require.

Example 4: When cystatin C helps

Cachectic patient, creatinine eGFR 80, clinical picture suggests worse

Result: Cystatin C confirms

Low muscle mass produces little creatinine, so creatinine-based eGFR overestimates function. Cystatin C is independent of muscle.

Common Mistakes

⚠️

Diagnosing CKD from eGFR alone in G1 or G2

Those values are normal. A CKD diagnosis at those stages requires evidence of kidney damage, usually albuminuria.

⚠️

Using an equation that still includes race

The 2021 CKD-EPI equation removed the race coefficient. Older versions could delay referral and transplant listing by overestimating function.

⚠️

Using eGFR for drug dosing

It is normalised to 1.73 m². Drug dosing requires absolute clearance, for which Cockcroft–Gault in mL/min is the usual basis.

⚠️

Trusting creatinine-based eGFR at body composition extremes

Amputees, bodybuilders and cachectic patients produce atypical amounts of creatinine. Cystatin C is preferred for confirmation.

Frequently Asked Questions

CKD-EPI vs MDRD?

CKD-EPI 2021: more accurate at normal/near-normal GFR. MDRD: older, underestimates above 60 mL/min. CKD-EPI 2021 removed race coefficient (2021 update). Preferred equation for adults without race adjustment.

When to use cystatin C?

Cystatin C less affected by muscle mass than creatinine. Use when: muscular bodybuilder (overestimates eGFR), muscle-wasting disease (underestimates), or equivocal creatinine-based result. Combined creatinine+cystatin: most accurate CKD-EPI equation.

Why was the race coefficient removed?

Because race is a social rather than biological category, and the coefficient overestimated kidney function in Black patients, potentially delaying referral and transplant listing.

Can CKD be diagnosed from eGFR alone?

Not at stages G1 and G2, where eGFR is normal. Evidence of kidney damage, usually albuminuria, is required alongside.

When should cystatin C be used?

When creatinine-based eGFR may mislead — extremes of muscle mass, amputation, cachexia — or to confirm a borderline result before a major clinical decision.

Should eGFR be used for drug dosing?

No. It is normalised to body surface area, which suits staging but not dosing. Absolute clearance in mL/min is what drug labelling uses.