What does it measure?
Estimated glomerular filtration rate is calculated, usually from creatinine, age, and sex. Some equations use cystatin C or combine both markers. It is an estimate rather than a direct measurement, commonly reported relative to a standard body surface area. [2]
Before reading the calculation
- Inputs
- An equation using blood creatinine, age, and sex; some equations also use cystatin C.
- Method
- Record which equation was used. Results from different equations may differ without a true change in the kidneys.
What can the result mean?
A lower result can indicate reduced filtration. One low value does not establish chronic kidney disease: chronicity generally requires relevant abnormalities for at least three months or other evidence of a lasting problem. A higher estimate is not automatically a sign of better kidney health, and normal filtration does not exclude albumin leakage. [1]
An equation using blood creatinine, age, and sex; some equations also use cystatin C.
- Method
- Record which equation was used. Results from different equations may differ without a true change in the kidneys.
When is it useful, and how is it read?
Kidney assessment combines filtration, urine albumin, and the trend over time. Evidence persisting for at least three months supports chronic kidney disease; a sudden decline calls for assessment of an acute change instead of waiting to establish chronicity. The cause and associated findings determine the next step. [1] [3]
Reading the results together
| Marker | What it adds |
|---|---|
| eGFR | Estimates how well blood is being filtered. |
| Microalbuminuria, Random Urine (Alb-Creat Ratio) | Looks for albumin leakage relative to urine concentration. |
A reassuring eGFR does not replace urine albumin. Reading both and their trends gives a fuller picture than one result alone. [3]
What can affect it?
Creatinine-based estimates can be less reliable with unusually high or low muscle mass, rapidly changing kidney function, pregnancy, or certain medicines. The equation and test method matter. Combining creatinine and cystatin C can improve accuracy when a treatment decision needs a clearer estimate. [1] [2]
Preserved filtration does not rule out kidney damage
eGFR estimates filtering ability. Kidney damage can still be present when filtration is preserved, for example when albumin leaks into urine, so a reassuring eGFR does not answer every kidney-health question. [3]
Questions you might have
Is eGFR a direct measurement of filtration?
No. It is an estimate, and the equation and blood markers affect its accuracy. Trends often provide more context than one result. [2]
Why read urine albumin when eGFR is reassuring?
Filtration and albumin leakage are different kidney questions. A reassuring filtration estimate does not describe every aspect of kidney health. [3]
What comes next?
Review eGFR with urine albumin-to-creatinine ratio, blood pressure, medicines, and previous results. Unexpected changes may need timely repeat testing rather than waiting three months to act. A clinician can distinguish a temporary change, an acute problem, and a persistent pattern. [1]
Is this estimate reliable for my body and current health, and how does it compare with urine albumin?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease
- NIDDK — Estimated Glomerular Filtration Rate Calculators
- NIDDK — Chronic Kidney Disease Tests & Diagnosis
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
