Estimated Glomerular Filtration Rate

Estimated glomerular filtration rate is a calculated estimate of how fast your kidneys filter blood, based mainly on your blood creatinine along with age and sex. It's the standard number doctors use to gauge overall kidney function. It's called 'estimated' because it's derived from an equation rather than measured directly, so the label on your lab report usually reads something like 'GFR, estimated' or 'eGFR'.

eGFR is reported in mL/min/1.73 m², meaning the milliliters of blood your kidneys filter per minute, standardized to an average adult body surface area of 1.73 square meters. Most labs simply write mL/min. Higher numbers mean better filtering capacity, and roughly 90 or above is considered normal kidney function.

Yes. An eGFR of 90 or higher is generally considered normal kidney function in the absence of other signs of kidney damage such as protein in the urine. Values of 60 to 89 are labeled 'mildly decreased' and are still common and often unremarkable in healthy adults, especially with age. Many labs stop reporting an exact number above 90 or 120 and just say 'greater than 60.'

Those values fall into the reduced-function range used to stage chronic kidney disease. Roughly: 45 to 59 is stage G3a, 30 to 44 is stage G3b, 15 to 29 is stage G4, and below 15 is stage G5. So an eGFR of 31 or 33 sits in stage G3b (moderately to severely decreased) and 22 sits in stage G4 (severely decreased). A single low reading should be confirmed and interpreted by a physician alongside urine tests and your history, since dehydration, illness, and lab timing can all move the number.

Both are equations that estimate GFR from creatinine, but CKD-EPI (introduced in 2009 and refined since) is more accurate at higher, near-normal eGFR values and is now the preferred standard in most labs. MDRD is the older equation and tends to underestimate GFR in people with better kidney function. If your reports come from different labs, part of any change in your eGFR could simply reflect a switch in the equation used, so it's worth checking which one your lab reports.

Yes, and this is common in lifters and men on TRT. Because standard eGFR is calculated from creatinine — a byproduct of muscle metabolism — more muscle mass and creatine supplementation can raise creatinine and mechanically lower the estimated eGFR without any real drop in kidney function. If your eGFR looks borderline but you're muscular or supplement creatine, ask for a cystatin-C-based eGFR, which doesn't depend on muscle mass and gives a fairer estimate.

For adults, an eGFR of 90 or above is considered normal, 60 to 89 is mildly decreased, and below 60 that persists for three months or more may indicate chronic kidney disease. eGFR naturally declines with age, so a value in the 60s or 70s in an older adult is not automatically a concern. Your physician interprets it together with urine albumin, blood pressure, and your overall clinical picture rather than the number alone.