A healthy eGFR is generally 90 or above, measured in mL/min/1.73m². In young, healthy adults, eGFR typically falls between 100 and 110. But “normal” depends heavily on your age, because kidney filtration naturally declines over time, and a number that looks concerning at 30 may be perfectly expected at 70.
What eGFR Actually Measures
Your eGFR (estimated glomerular filtration rate) is a calculation of how well your kidneys filter waste from your blood each minute. It’s derived from a simple blood test that measures creatinine, a waste product your muscles produce at a fairly steady rate. Healthy kidneys clear creatinine efficiently, so when it builds up in your blood, it signals that your kidneys aren’t filtering as well as they should. The current standard formula, updated in 2021, uses your creatinine level, age, and sex to produce the estimate. Race is no longer factored in.
How eGFR Changes With Age
Kidney function peaks in your 20s and gradually declines from there. This is normal aging, not disease. Data from a large healthy Dutch population illustrates this well: at ages 25 to 29, the low end of normal (the 5th percentile) is around 94 for men and 85 for women. By ages 50 to 54, those low-normal values drop to 67 and 70. And by ages 70 to 74, they fall to 44 and 51.
This matters because a 72-year-old with an eGFR of 50 is in a very different situation than a 35-year-old with the same number. The older person may have entirely normal kidney function for their age, while the younger person likely has something worth investigating. Context is everything with this test.
The CKD Staging System
Doctors use eGFR to classify chronic kidney disease into five stages:
- Stage 1: eGFR 90 or above, with other signs of kidney damage (such as protein in urine)
- Stage 2: eGFR 60 to 89, with signs of kidney damage
- Stage 3a: eGFR 45 to 59
- Stage 3b: eGFR 30 to 44
- Stage 4: eGFR 15 to 29
- Stage 5: eGFR below 15, which indicates kidney failure
A key detail: stages 1 and 2 require additional evidence of kidney damage beyond a low eGFR alone. An eGFR of 80 without protein in the urine or structural abnormalities isn’t automatically stage 2 CKD. At stage 3 and below, the eGFR number alone is enough to qualify as chronic kidney disease. Stage 5, with an eGFR under 15, is when kidney transplant evaluation and dialysis enter the conversation.
What Can Throw Off Your Results
Because eGFR is calculated from creatinine, anything that changes your creatinine level will shift the result, sometimes significantly. Higher creatinine makes your eGFR appear lower than your actual kidney function, which can create a false alarm.
Several common factors can temporarily raise creatinine and artificially lower your eGFR:
- High muscle mass: Bodybuilders and very muscular people produce more creatinine at baseline, so their eGFR often reads lower than their true kidney function.
- Creatine supplements: Creatine breaks down into creatinine, so supplementation can push your levels up.
- Recent intense exercise: A hard workout in the hours before a blood draw can elevate creatinine.
- Eating large amounts of cooked meat: Cooking converts compounds in meat into creatinine. Some labs will ask you to skip cooked meat the night before testing.
- Certain medications: Some drugs interfere with creatinine clearance without actually affecting kidney function.
If any of these apply to you and your eGFR comes back lower than expected, your doctor may repeat the test under more controlled conditions or order a different type of test.
When a Cystatin C Test Gives Better Answers
For some people, the standard creatinine-based eGFR just isn’t accurate enough. In these cases, doctors can order a test based on a different blood marker called cystatin C, which isn’t influenced by muscle mass or diet.
This is especially useful for older adults, people with very high or very low muscle mass, and those with multiple chronic conditions. Research in older adults found that when the two estimates disagree, taking the lower of the two values tends to be the most accurate. In that study, accuracy (meaning the estimate fell within 30% of actual measured kidney function) reached 92 to 94% when the right version was used. People whose cystatin C-based eGFR was lower than their creatinine-based eGFR tended to have lower muscle mass and more health issues overall, which helps explain why creatinine alone can miss declining kidney function in those groups.
eGFR in Children
Children follow a completely different trajectory. Newborns start with very low kidney filtration, around 20 mL/min/1.73m², because their kidneys are still maturing. At birth, creatinine levels actually reflect the mother’s kidney function rather than the baby’s, due to how blood is shared through the placenta. Kidney function rises rapidly over the first two years of life and reaches adult levels (roughly 120 mL/min/1.73m²) by about age two. Pediatric eGFR is calculated with different formulas than the adult version, so the numbers aren’t directly comparable.
What a Single eGFR Result Means
One eGFR reading is a snapshot, not a diagnosis. Kidney function fluctuates day to day based on hydration, diet, medications, and activity level. A single result below 60 doesn’t automatically mean chronic kidney disease. The standard practice is to confirm with repeat testing over at least 90 days before drawing conclusions. If your eGFR is consistently in the 60 to 89 range with no protein in your urine and no other signs of kidney problems, your kidneys are likely functioning fine, particularly if you’re over 40.
The trend over time matters more than any single number. A stable eGFR of 55 in a 70-year-old is far less concerning than an eGFR that drops from 85 to 55 over two years in anyone. If you’ve had the test done more than once, comparing results gives a much clearer picture than fixating on one value.