eGFREstimated glomerular filtration rate
An estimate of how fast your kidneys are filtering blood, calculated rather than measured.
eGFR stands for estimated glomerular filtration rate: roughly, how many millilitres of blood your kidneys clear each minute. It is not measured directly. It is calculated from your blood creatinine along with your age and sex, using a published equation, and reported per 1.73m² of body surface area so results compare between people of different sizes.
It matters because it is the number kidney function is usually described with, and because it is a rate rather than a substance. A value that falls over years means something different from a single low reading, which can follow dehydration, a very high protein intake or a hard training block, all of which shift creatinine without the kidneys being damaged.
In practice eGFR is read together with the creatinine it came from and with urine tests, never alone. Because it is calculated from muscle-derived creatinine, very muscular people can read lower and people with little muscle higher, without either reflecting kidney disease.