A good eGFR is 90 or above, which indicates normal kidney function. The number represents how many milliliters of blood your kidneys filter per minute, so a higher number means your kidneys are working more efficiently. Most people see this result on routine blood work and want to know whether their number is cause for concern or perfectly fine.
What eGFR Actually Measures
Your kidneys contain tiny clusters of blood vessels called glomeruli that act as filters. Every minute, they sift waste products and extra water out of your blood and send them out through urine. An eGFR test estimates how quickly that filtering is happening. It’s calculated from a blood test that measures creatinine, a waste product your muscles produce at a fairly steady rate. When your kidneys aren’t filtering well, creatinine builds up in the blood, and your eGFR drops.
The “e” stands for estimated. The lab plugs your creatinine level, age, and sex into a formula called the CKD-EPI 2021 equation. This updated formula, recommended by the National Kidney Foundation and the American Society of Nephrology, no longer includes a race coefficient, which was removed because it could lead to inaccurate results for some patients.
eGFR Ranges and What They Mean
Kidney function is divided into stages based on your eGFR number:
- 90 or above: Normal kidney function. You can still have kidney damage at this level (for example, protein in your urine), but the kidneys themselves are filtering properly.
- 60 to 89: Mildly reduced function. Many people in this range have no symptoms and may never develop kidney problems, especially if the number reflects normal aging.
- 45 to 59 (Stage 3a): Mild to moderate loss of function. This is typically when monitoring becomes more frequent.
- 30 to 44 (Stage 3b): Moderate to severe loss of function.
- 15 to 29: Severe loss of function. Several guidelines recommend referral to a kidney specialist when eGFR falls below 30.
- Below 15: Kidney failure. At this point, dialysis or a transplant may be necessary.
Why Your eGFR Drops With Age
Kidney function naturally declines as you get older, even in completely healthy people. Research measuring actual kidney filtration rates found that women lose roughly 0.96 mL/min per year, while men lose about 1.20 mL/min per year. That means a healthy 70-year-old could have an eGFR in the 70s or low 80s without having kidney disease. The decline in men also tends to accelerate at older ages rather than staying steady.
This is why a single eGFR reading doesn’t tell the whole story. A 75-year-old with an eGFR of 68 is in a very different situation than a 35-year-old with the same number. Your doctor will look at the trend over time, not just one snapshot.
Factors That Skew Your Results
Because eGFR is calculated from creatinine, anything that changes your creatinine level can make the number look better or worse than your kidneys actually are. Muscle mass is the biggest factor. People with a lot of muscle produce more creatinine naturally, which can make their eGFR appear lower than it truly is. Conversely, someone with very low muscle mass, such as an elderly person or someone who’s been bedridden, may get an eGFR that looks reassuringly normal even when kidney function is slipping.
A very high-protein diet can also temporarily raise creatinine levels. Certain medications interfere with how creatinine is handled by the kidneys, pushing the number in one direction without any real change in kidney health. If your result seems off, your doctor may order a second type of test that measures a different protein called cystatin C. This marker is less influenced by muscle mass and diet, and recent guidelines have encouraged its use, especially for people with borderline results. Studies show it tends to be more accurate than creatinine-based estimates, particularly in the high-normal range and in people with diabetes.
What a Borderline Result Means for You
An eGFR between 60 and 89 is the most common “borderline” range that prompts questions. In many cases, particularly for people over 50, a number in this range reflects age-related decline rather than disease. The key distinction is whether there are other signs of kidney damage. If your urine shows protein, if you have high blood pressure or diabetes, or if your eGFR is trending downward on repeated tests, that combination matters more than the single number.
A stable eGFR of 65 in someone who is 72 years old with no protein in their urine is very different from a dropping eGFR of 65 in a 45-year-old with diabetes. Context determines whether the number is reassuring or a signal to act. Repeated testing every few months helps distinguish a temporary dip from a genuine decline, and comparing creatinine-based eGFR with a cystatin C-based eGFR can help resolve uncertainty in ambiguous cases.
How the Test Works
An eGFR isn’t a separate test you need to schedule. It’s calculated automatically from a basic metabolic panel or comprehensive metabolic panel, which are standard blood draws. A lab technician takes a small blood sample from your arm, measures the creatinine level, and the lab’s computer applies the CKD-EPI formula to generate your eGFR. Results typically come back within a day or two. No special preparation like fasting is universally required for the creatinine portion of the test, though your lab may have specific instructions if other tests are being run at the same time.
If you’re tracking your kidney health over time, try to get your blood drawn under similar conditions each time. Intense exercise the day before, significant changes in hydration, or a large high-protein meal can all nudge creatinine levels enough to shift your eGFR by a few points.