Finding the right tests…
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Finding the right tests…
Biochemistry
A GFR test doesn't measure your kidneys directly — it estimates how many millilitres of blood they filter each minute, using your blood creatinine level combined with your age and sex. Because creatinine is a waste product that healthy kidneys clear efficiently, a rising creatinine level, and therefore a falling GFR, usually means filtering capacity is declining, even before other symptoms show up. Doctors use this estimate, called eGFR, both to screen for kidney disease in people with no symptoms and to track how existing kidney disease is progressing over months or years. A single reading matters less than the trend across repeat tests.
This test estimates the volume of blood your kidneys filter each minute, reported in mL/min/1.73m². It's calculated rather than measured directly, using your creatinine level along with factors like age and sex, since creatinine builds up in the blood as filtering capacity drops. The result is usually tracked over time rather than judged from one draw, because a single value can be affected by muscle mass, recent illness, or dehydration.
Your kidneys don't get scanned or weighed for this test. Instead, the lab measures creatinine — a waste product your muscles produce at a fairly steady rate — and plugs it into a formula along with your age and sex to estimate how much blood your kidneys are filtering each minute.
An eGFR of 60 or higher generally falls in the normal range. Below 60 can point to kidney disease, and the lower the number goes, the more advanced that disease is likely to be. An eGFR of 15 or below is classed as kidney failure, at which point most people need dialysis or a transplant.
A single eGFR reading can be thrown off by dehydration, a recent illness, or unusually high or low muscle mass, since the calculation relies on creatinine. That's why doctors usually watch the trend across repeat tests rather than acting on one number, especially in someone with no other signs of kidney trouble.
eGFR is ordered both to screen people who have no kidney symptoms but are at higher risk — from diabetes or high blood pressure, for instance — and to monitor people already diagnosed with chronic kidney disease, including before starting medicines that are hard on the kidneys.
An eGFR of 60 or higher is generally considered within the normal range. Below 60 for three months or more is a sign of chronic kidney disease, and ranges can vary slightly by lab, so read your result against the figure on your own report.
A lower eGFR means your kidneys are filtering less blood each minute than expected, which usually points to reduced kidney function. An eGFR of 15 or below is considered kidney failure and needs prompt medical attention.
No. It's an estimate calculated from your blood creatinine level along with factors like age and sex, not a direct scan or measurement of kidney tissue. That's why it's called eGFR — estimated GFR.
Yes. Dehydration, a recent illness, or certain medicines can lower a single eGFR reading without reflecting a lasting change in kidney function. Your doctor will usually repeat the test to see if the result holds over time.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes, eGFR tends to decline somewhat with age even in otherwise healthy kidneys, and the formula used accounts for this. Your doctor interprets your number in the context of your age rather than against a single fixed target.
Generally, the goal with a lowered GFR is to prevent it from dropping further rather than to raise it back up, by managing conditions like diabetes and blood pressure. Ask your doctor what's realistic for your specific situation.