Normal kidney function is primarily measured by a number called eGFR (estimated glomerular filtration rate), and a result of 60 or higher is considered normal. But your lab report likely includes several other kidney-related numbers, each telling a slightly different part of the story. Here’s what each one means and where your results should fall.
eGFR: The Most Important Number
Your eGFR estimates how well your kidneys filter waste from your blood each minute. It’s calculated from a blood test for creatinine, factoring in your age and sex. A result of 60 or higher falls in the normal range, while a result below 60 may indicate kidney disease. A result of 15 or lower suggests kidney failure.
Healthy young adults typically have an eGFR between 100 and 110. But this number naturally declines with age, and that’s not necessarily a sign of disease. In a large study of healthy Dutch adults, the lower end of normal eGFR was around 90 at ages 25 to 29, dropped to roughly 67 to 70 by ages 50 to 54, and fell to 44 to 51 by ages 70 to 74. So an eGFR of 55 in a 72-year-old means something very different than the same number in a 35-year-old. For adults under 40, kidney specialists generally consider an eGFR below 75 to be concerning.
One important recent change: labs used to adjust eGFR calculations based on race, producing different results for Black patients. In 2021, the National Kidney Foundation and the American Society of Nephrology recommended removing the race variable from the equation entirely, recognizing that race is a social construct rather than a biological one. Most labs in the U.S. have now adopted the updated formula.
Creatinine: What Your Muscles Reveal
Creatinine is a waste product your muscles produce at a fairly steady rate. Your kidneys filter it out, so when they’re working well, blood creatinine stays low. The normal range is 0.7 to 1.3 mg/dL for men and 0.5 to 0.95 mg/dL for women.
The catch is that creatinine levels don’t just reflect kidney function. They’re also heavily influenced by muscle mass. Someone who is very muscular or physically active can have creatinine levels that look elevated even though their kidneys are perfectly fine. The reverse is also true: a person with low muscle mass (due to aging, illness, or a sedentary lifestyle) may have creatinine in the “normal” range even when their kidneys are significantly impaired.
Diet plays a role too. Eating a lot of meat or taking creatine supplements can push creatinine levels higher independently of kidney health. This is one reason doctors look at eGFR (which adjusts for some of these variables) rather than creatinine alone.
BUN: Blood Urea Nitrogen
BUN measures the amount of urea nitrogen, a waste product from protein digestion, in your blood. The normal range is 5 to 20 mg/dL. When your kidneys aren’t filtering efficiently, BUN rises.
Like creatinine, BUN isn’t a perfect standalone measure. It can increase from eating a high-protein diet, dehydration, or certain medications, none of which involve actual kidney damage. Doctors often look at BUN alongside creatinine. In someone with kidney problems, BUN and creatinine tend to rise in roughly a 10-to-1 ratio. If BUN climbs disproportionately higher than that ratio would predict, the cause is often something outside the kidneys, like dehydration or gastrointestinal bleeding. A lower-than-expected ratio can point to low protein intake or liver disease.
Urine Albumin: Detecting Early Damage
Even when eGFR looks fine, your kidneys could have early damage that shows up in a urine test. Albumin is a protein that healthy kidneys keep in the blood. When the filtering units are injured, small amounts leak into urine. The standard test reports a urine albumin-to-creatinine ratio (ACR):
- Below 30 mg/g: normal
- 30 to 300 mg/g: moderately increased albumin (sometimes called microalbuminuria), a sign of early kidney damage
- Above 300 mg/g: severely increased albumin, indicating more significant kidney injury
This test is especially important for people with diabetes or high blood pressure, since both conditions can silently damage the kidneys long before eGFR drops. Finding albumin in the urine early gives you a window to slow or prevent further progression through blood pressure control and other treatments.
Cystatin C: A More Precise Alternative
If your doctor suspects that creatinine isn’t giving an accurate picture, perhaps because you’re very muscular, very thin, or elderly, they may order a cystatin C test. Cystatin C is a small protein produced by nearly all cells in the body at a constant rate, and unlike creatinine, it isn’t affected by muscle mass, diet, or physical activity. The normal serum range is roughly 0.47 to 1.03 mg/L.
Research has shown that cystatin C can detect mild drops in kidney function that creatinine-based tests miss. In one study, cystatin C levels started rising above normal when filtration dropped below about 94 mL/min, while creatinine was still sitting comfortably in the normal range. Current guidelines recommend using cystatin C to confirm kidney disease in people who are at risk or whose creatinine-based eGFR falls in a borderline zone.
Bicarbonate: A Sign of Kidney Balance
Your kidneys help regulate the acid-base balance of your blood by managing bicarbonate levels. The normal serum bicarbonate range is 22 to 29 mEq/L. When kidney function declines, the body has trouble clearing acid, and bicarbonate can drop below 22. Kidney specialists flag that threshold because low bicarbonate is linked to faster progression of kidney disease and muscle wasting. It’s not typically part of a basic screening panel, but it appears on a comprehensive metabolic panel and becomes more relevant if you already have known kidney issues.
What These Numbers Look Like Together
No single number tells the full story. A complete picture of kidney health combines at least eGFR (from a blood creatinine test) with a urine albumin test. Someone can have a normal eGFR but elevated urine albumin, meaning early damage is present. Someone else might have a low eGFR due entirely to age, with no albumin in the urine and no progressive disease.
Chronic kidney disease is staged using both measures. Stages 1 and 2 involve an eGFR above 60 but with evidence of kidney damage like abnormal albumin levels. Stage 3 begins when eGFR drops below 60, stage 4 below 30, and stage 5 below 15. Context matters enormously at every stage: your age, the trend over time (is the number stable or dropping?), and whether there are signs of damage in the urine all shape what the numbers actually mean for you.
If you’re reviewing your own lab results, the most useful thing you can do is compare your current numbers to previous ones. A single snapshot is far less informative than a trend showing whether your kidney function is stable, gradually declining with normal aging, or dropping faster than expected.