What is GFR?
The Glomerular Filtration Rate (GFR) is the definitive test used by medical professionals to check how well your kidneys are working. Specifically, it estimates how much blood passes through the glomeruli (tiny filters in the kidneys that extract waste from your blood) each minute.
Understanding the 2021 CKD-EPI Equation
Because measuring a person's exact GFR requires a highly complex and invasive medical procedure, doctors almost exclusively rely on an estimated GFR (eGFR). This is calculated using a mathematical formula that takes into account your age, biological sex, and the level of creatinine in your blood.
Creatinine is a chemical waste product generated from typical muscle metabolism. Healthy kidneys filter creatinine out of the blood and excrete it in urine. If kidney function begins to decline, creatinine levels in the blood will rise.
Note on Race: In 2021, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) formed a joint task force to update the eGFR equation. They officially recommended the removal of the "race modifier" (which previously adjusted scores for Black individuals) in favor of the new 2021 CKD-EPI formula used by this calculator.
Stages of Chronic Kidney Disease (CKD)
Based on the eGFR output, medical professionals categorize kidney health into five distinct stages:
| Stage | eGFR Value | Description |
|---|---|---|
| Stage 1 | 90 or higher | Normal or high function (with other evidence of kidney damage) |
| Stage 2 | 60 to 89 | Mildly decreased kidney function |
| Stage 3a | 45 to 59 | Mild to moderately decreased function |
| Stage 3b | 30 to 44 | Moderate to severely decreased function |
| Stage 4 | 15 to 29 | Severely decreased function (Preparation for dialysis) |
| Stage 5 | Less than 15 | Kidney failure (End-stage renal disease) |