What eGFR is
Glomerular filtration rate (GFR) is how much blood your kidneys filter each minute. Measuring it directly is complicated, so labs estimate it (eGFR) from a blood test for creatinine, a waste product from muscle. It's reported in mL/min/1.73 m², meaning scaled to an average adult body size. Higher is better; in adults a normal eGFR is usually above 90, and it falls gradually with age even in healthy people.
The CKD-EPI 2021 equation
Scr is serum creatinine in mg/dL. κ is 0.7 for females and 0.9 for males; α is −0.241 for females and −0.302 for males. To convert creatinine from µmol/L to mg/dL, divide by 88.4. This version, published in 2021, removed the race coefficient used in older equations; the NKF recommends labs use it for adults.
Worked example
A 60-year-old man with creatinine 1.2 mg/dL: Scr/κ = 1.2/0.9 = 1.333, which is above 1, so the min term is 1 and the max term is 1.333−1.200 = 0.7081. Then 0.993860 = 0.6886, and 142 × 0.7081 × 0.6886 = 69.2, reported as 69 mL/min/1.73 m². That falls in category G2.
GFR categories
| Stage | eGFR | What it means |
|---|---|---|
| G1 | 90 or higher | Normal or high. CKD only if there's also kidney damage, such as albumin in the urine (uACR 30 or higher), for 3 months or more |
| G2 | 60–89 | Mildly decreased. CKD only with signs of kidney damage for 3 months or more |
| G3a | 45–59 | Mild to moderate loss of kidney function |
| G3b | 30–44 | Moderate to severe loss |
| G4 | 15–29 | Severe loss |
| G5 | Less than 15 | Kidney failure, or on dialysis |
The stages describe results that last 3 months or more. A single low reading can be temporary, so tests are usually repeated before anyone is diagnosed.
Important: it's an estimate
This is a general estimate from a published formula, not medical advice, and it doesn't replace your lab report or your doctor. Talk to your doctor about what your number means for you. eGFR from creatinine can be less accurate with unusually high or low muscle mass, pregnancy, age over 70, cirrhosis, nephrotic syndrome, a past organ transplant, some medicines, or when kidney function is changing quickly. It isn't for children under 18. When an accurate number matters, for example for drug dosing, doctors may add a cystatin C test; NIDDK notes that combining creatinine and cystatin C is more accurate than creatinine alone. Trends over time often say more than one value.