serum creatinine · estimated glomerular filtration rate · kidney function
Creatinine and eGFR: what your kidney result means
Creatinine is muscle waste that healthy kidneys clear. eGFR turns that number into an estimate of how well they are filtering — and "estimate" is the important word.
What it measures
Creatinine is produced at a fairly steady rate by muscle and removed almost entirely by the kidneys, so what is left in the blood reflects how well they are filtering. eGFR converts that into an estimated filtration rate using your age and sex, which is easier to interpret than creatinine on its own.
Why it gets tested
In routine health checks, before and during medication cleared by the kidneys, in diabetes and high blood pressure — the two commonest causes of kidney disease — and to investigate swelling, changes in urination or an abnormal urine test. It is also checked before imaging with contrast.
Typical ranges
Creatinine runs roughly 60–110 µmol/L (0.7–1.3 mg/dL) in men and 45–90 µmol/L (0.5–1.0 mg/dL) in women, because it depends on muscle mass. eGFR is reported in mL/min/1.73 m²: 90 or above is normal, 60–89 mildly reduced, and below 60 sustained for three months is what defines chronic kidney disease.
Compare against the range printed on your own report, not this one. Laboratories differ, and yours is the one your doctor is reading.
What a high result can mean
Less is being cleared — which can be acute (dehydration, infection, a recently started NSAID or ACE inhibitor, an obstruction) or chronic kidney disease. It also rises with large muscle mass, a high-protein or creatine-supplemented diet, and after a big meal of cooked meat, none of which is a kidney problem at all.
What a low result can mean
Usually little muscle rather than exceptional kidneys — seen in older people, in prolonged illness, in malnutrition, and in pregnancy, where filtration genuinely does increase. In those situations eGFR overstates kidney function, because the formula assumes an average relationship between muscle and creatinine.
What moves it
Muscle mass, pregnancy, hydration, meat eaten in the previous hours, creatine supplements, and several common drugs — trimethoprim and cimetidine raise measured creatinine without affecting filtration at all. Current UK and US practice has removed the race coefficient from eGFR equations, so an older report may not be directly comparable with a new one.
What usually happens next
A single abnormal result is repeated, usually alongside a urine albumin-to-creatinine ratio, because protein in the urine says more about outlook than the filtration number does. A reduction sustained for three months or more is chronic kidney disease, and leads to a review of blood pressure, diabetes control and every drug the kidney has to clear.
Common questions
Is a low eGFR the same as kidney failure?
No. An eGFR between 60 and 89 is common and often stable, particularly with age. Chronic kidney disease is defined by a reduction sustained for at least three months, and most of it never progresses to failure — especially where blood pressure and diabetes are well managed.
Can the gym change my creatinine?
Yes. Muscle mass, creatine supplements, a heavy training session and a large meat meal all raise creatinine without anything being wrong with the kidneys. Mentioning it to whoever ordered the test makes the result far easier to read.