eGFR (estimated glomerular filtration rate) is an estimate of how well the kidneys filter blood. It is reported as mL/min/1.73 m² (normalized to a standard body surface area).

eGFR is commonly calculated from serum creatinine along with age and sex (and sometimes race, depending on the equation).

eGFR is standardized to a body surface area (BSA) of 1.73 m², historically considered an average adult BSA. This allows easier comparison across individuals.

In very small or very large body size, clinicians may consider adjusting to actual BSA if needed.

Common adult eGFR categories (GFR stages):

• ≥ 90: Stage 1* (Normal / High)
• 60–89: Stage 2* (Mildly reduced)
• 45–59: Stage 3a (Mild–moderate decrease)
• 30–44: Stage 3b (Moderate–severe decrease)
• 15–29: Stage 4 (Severe kidney impairment)
• < 15: Stage 5 (Kidney failure)

*Stages 1–2 require evidence of kidney damage (e.g., albuminuria) despite preserved eGFR.

Most adult creatinine-based equations use:

• Serum creatinine (Scr)
• Age
• Sex
• Race (only in older equations like MDRD and CKD-EPI 2009)

The commonly used adult MDRD (IDMS-traceable) form is:

Scr is serum creatinine in mg/dL. MDRD is less accurate at higher GFR (near-normal kidney function).

CKD-EPI 2009 uses sex-specific constants (κ, α):

Where: for females κ=0.7, α=−0.329; for males κ=0.9, α=−0.411. Scr in mg/dL.

CKD-EPI 2021 is a newer race-free creatinine equation:

Where: for females κ=0.7, α=−0.241; for males κ=0.9, α=−0.302. Scr in mg/dL.

They differ because they were derived from different datasets and use different coefficients. CKD-EPI equations generally perform better than MDRD, especially at higher GFR.

CKD-EPI 2021 is race-free, so values may differ from CKD-EPI 2009 in individuals previously categorized as “Black” in older equations.

Creatinine-based eGFR may be less reliable in:

• Rapidly changing kidney function (acute kidney injury)
• Extremes of muscle mass (very muscular or very low muscle mass)
• Pregnancy
• Severe liver disease or malnutrition
• Conditions affecting creatinine production or secretion

In such situations, clinicians may use cystatin C, measured clearance, or other approaches.

Not exactly. Creatinine clearance (CrCl) estimates clearance from urine/serum measurements or formulas like Cockcroft–Gault, while eGFR is a standardized estimate normalized to 1.73 m².

Many drug dosing recommendations still reference Cockcroft–Gault CrCl in adults.

Yes. CKD diagnosis is based on duration (≥3 months) plus either reduced eGFR or evidence of kidney damage.

Evidence of kidney damage may include albuminuria (e.g., elevated ACR), abnormal imaging, or persistent urinary abnormalities.

CKD-EPI equations use: min(Scr/κ, 1) and max(Scr/κ, 1) to apply different slopes below and above a creatinine threshold.

This improves accuracy across a wider range of creatinine values compared with a single exponent model.

Common conversion:

Always confirm the unit reported by your laboratory before using any calculator.

Older equations (MDRD, CKD-EPI 2009) include a race factor. The newer CKD-EPI 2021 equation is race-free and is increasingly adopted.

Choice of equation may depend on local guidelines, lab reporting practices, and clinical context.

Interpret eGFR alongside: symptoms, urinalysis (protein/albumin), blood pressure, comorbidities, imaging, and trend over time. A single eGFR is a snapshot; persistent abnormalities matter most.

This FAQ section is for education only and does not replace clinical judgement or specialist advice.

This FAQ section is for education only and does not replace clinical judgement or specialist advice.