A more accurate, but still not perfect, estimate of kidney function is a calculation of your estimated glomerular filtration rate (GFR). GFR is generally accepted as the best overall index of kidney function and is one that the NKF encourages clinicians to use. Studies suggest GFR identifies CKD in its early stages better than other creatinine-based tests.
In a nutshell, GFR is the rate at which all of the nephrons in your kidneys filter a substance from your blood. The more functioning, healthy nephrons you have, the better the per-minute filtration rate and the higher the GFR. The lower the GFR, the poorer the kidney function.
Normal kidneys filter out most of the creatinine in the blood at a fixed rate:
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