ENKIKnowledge libraryTests & results
What does eGFR mean?
eGFR is an estimate of how much blood the kidneys filter each minute, adjusted to a standard body surface area. It is calculated rather than measured directly, so it should be read as an informed estimate with a range of uncertainty.
This guide helps you understand terms and prepare questions. It cannot diagnose a condition or tell you to change treatment. Seek local medical care for urgent or severe symptoms.
Start here
Three points to keep
- eGFR is usually calculated from serum creatinine plus demographic information.
- The trend is often more informative than a small change between two tests.
- Urine ACR and the clinical picture add information eGFR cannot show.
What the number estimates
Glomerular filtration rate describes filtration by the kidney's microscopic filters. Direct measurement is complex, so laboratories usually estimate it from creatinine in the blood using a validated equation.
The result is reported as mL/min/1.73 m². The 1.73 m² is a standard body surface area used to compare kidney function across adults; it is not the person's actual body size.
Why creatinine can mislead
Creatinine is affected by more than kidney filtration. The estimate may be less reliable when creatinine production or distribution differs substantially from the population used to build the equation.
- Very high or low muscle mass, amputation, paralysis, or severe frailty
- Recent cooked-meat intake, creatine supplements, or intense exercise
- Rapidly changing kidney function during acute illness
- Pregnancy or unusual body size
- Medicines that change creatinine handling without changing true filtration
When another marker helps
Cystatin C is another blood marker used to estimate GFR. A clinician may combine creatinine and cystatin C when greater precision could change a decision or when creatinine may be unreliable.
Neither estimate replaces the full assessment. Urine albumin, blood pressure, imaging, symptoms, medicines, and the underlying cause remain important.
Reading a trend
Compare results taken under reasonably similar conditions and note illness, dehydration, medication changes, or hospital care. A small movement does not automatically mean permanent progression.
A large or unexpected fall, especially with reduced urine, swelling, vomiting, breathlessness, confusion, or acute illness, needs prompt clinical assessment rather than waiting for the next routine check.
For your next visit
Questions worth taking with you
- 01Is creatinine-based eGFR likely to be reliable for my body composition and situation?
- 02Would cystatin C or a repeat test change an important decision?
- 03What rate of change would prompt earlier review?
Evidence trail
Sources
ENKI prioritizes current clinical guidelines and public-health sources. Links open on the publisher's website.
Published by the ENKI Health Editorial Team under our editorial policy.