Estimated GFR (eGFR) is a number on your blood test that shows how well your kidneys are filtering waste from your blood. It’s measured in milliliters per minute, and a result of 90 or above is generally considered normal. Your doctor uses this number to screen for kidney disease, track kidney function over time, and determine if any damage has occurred.
What eGFR Actually Measures
Your kidneys contain tiny filtering units called glomeruli. Every minute, these filters clean a certain volume of blood, removing toxins and excess fluid that leave your body as urine. Your eGFR estimates how many milliliters of blood those filters clean per minute. A higher number means your kidneys are working well. A lower number means filtration has slowed down, and waste products may be building up in your blood.
The test itself is a standard blood draw. The lab measures a waste product called creatinine, which your muscles produce at a fairly steady rate. Healthy kidneys clear creatinine efficiently, so when levels rise in your blood, it signals that your kidneys aren’t filtering as well as they should. The lab then plugs your creatinine level into a formula along with your age and sex to calculate your eGFR. You don’t need to do anything special for this test, though your provider may ask you to fast or avoid certain foods for a few hours beforehand.
A notable change happened in 2021: the National Kidney Foundation and American Society of Nephrology recommended removing race as a variable from the standard eGFR equation used in the United States. Labs now use a race-free formula called the CKD-EPI equation, which provides a single result regardless of the patient’s racial background.
What a Normal eGFR Looks Like
An eGFR of 90 or above is considered normal kidney function. But “normal” shifts as you age. A healthy 20-year-old typically has an eGFR around 99 to 101. By age 80, the average drops to about 63 to 66, even without kidney disease. That natural decline happens because kidneys gradually lose some filtering capacity over a lifetime.
For context, a large European study found that at age 20, the middle-of-the-road eGFR was about 99 for men and 101 for women. At age 80, those midpoints dropped to 66 for men and 63 for women. The range of normal is also wide: a healthy 20-year-old could have an eGFR anywhere from about 78 to 121, while a healthy 80-year-old might fall between 46 and 84. So a result in the 60s or 70s for someone over 70 doesn’t automatically mean something is wrong.
How eGFR Maps to Kidney Disease Stages
Doctors use eGFR to classify chronic kidney disease (CKD) into five stages, according to the National Kidney Foundation:
- Stage 1 (eGFR 90 or above): Normal filtration, but other signs of kidney damage may be present, like protein in the urine.
- Stage 2 (eGFR 60 to 89): Mild loss of function. Many people in this range have no symptoms at all.
- Stage 3a (eGFR 45 to 59): Mild to moderate loss of function.
- Stage 3b (eGFR 30 to 44): Moderate to severe loss of function.
- Stage 4 (eGFR 15 to 29): Severe loss of function.
- Stage 5 (eGFR below 15): Kidney failure, where dialysis or transplant becomes necessary.
A single eGFR reading doesn’t define your stage. Doctors typically repeat the test over several months to see whether the number is stable or trending downward. A temporarily low result can happen during illness, dehydration, or after eating a large amount of protein.
What Low eGFR Feels Like
This is the tricky part: early kidney disease (stages 1 through 3) usually causes no symptoms at all. That’s why routine blood work catches it before you’d ever notice a problem on your own. Most people with an eGFR in the 45 to 89 range feel completely fine.
Symptoms tend to appear in later stages, when filtration has dropped significantly. These can include nausea, loss of appetite, muscle cramps, swelling in the feet and ankles, dry and itchy skin, trouble sleeping, shortness of breath, and urinating much more or much less than usual. None of these are specific to kidney disease alone, which is why the blood test matters more than how you feel.
When the Test Can Be Inaccurate
Because eGFR relies on creatinine, anything that changes your creatinine level for reasons unrelated to your kidneys can throw the estimate off. Creatinine comes from muscle, so people with unusually high or low muscle mass get less reliable results. Bodybuilders tend to have higher creatinine (making eGFR look artificially low), while frail older adults or people with muscle-wasting conditions may have lower creatinine (making eGFR look artificially high, masking real kidney problems).
Other situations where creatinine-based eGFR becomes less reliable include pregnancy, acute illness requiring hospitalization, amputations, paraplegia, extreme diets (especially very low-meat or vegetarian diets), and rapidly changing kidney function. In these cases, the number on your lab report may not reflect your true filtration rate.
The Cystatin C Alternative
When creatinine isn’t reliable enough, doctors can order a second blood marker called cystatin C. Unlike creatinine, cystatin C isn’t affected by muscle mass, making it useful for people at the extremes of body composition. The most accurate estimate of kidney function uses both creatinine and cystatin C together, which is generally accepted as closer to actual measured GFR than either marker alone.
Kidney disease guidelines recommend measuring cystatin C for confirmatory testing whenever creatinine-based results seem inconsistent with a patient’s clinical picture. Despite this, cystatin C testing is still underused. It has its own limitations: steroid use, thyroid problems, obesity, and inflammation can all push cystatin C levels higher independent of kidney function. But combining both markers helps cancel out the blind spots of each individual test.
What to Make of Your Result
If your eGFR comes back at 60 or above and you have no protein in your urine, your kidneys are likely functioning well. If it’s between 60 and 89, your doctor may simply recheck it at your next physical to make sure it’s stable, especially if you’re over 60 and the number fits the expected range for your age.
An eGFR below 60 on two or more tests spread over at least three months meets the clinical definition of chronic kidney disease. That doesn’t necessarily mean your kidneys are failing. Many people live for decades in stage 3 without ever progressing further, particularly when underlying causes like high blood pressure or diabetes are well managed. The number is a starting point for a conversation about what’s driving the decline and what you can do to protect the kidney function you still have.