Glomerular filtration rate

Glomerular filtration rate (GFR) is the volume of fluid filtered from blood into kidney nephrons per unit time. It measures kidney filtration, usually estimated from blood markers rather than measured directly.

Glomerular filtration: The movement of water and small solutes from glomerular capillaries into the nephron, across a filtration barrier. GFR quantifies the rate of this movement across the kidney’s filtration barrier.
Chronic kidney disease: A persistent abnormality of kidney structure or function that has health implications. GFR helps define and stage chronic kidney disease when reduced over time.
Nephron: The kidney’s microscopic functional unit, consisting of a filtering corpuscle and a tubular system. Each nephron contains a glomerulus that contributes to the kidney’s total filtration rate.
Renal function reserve: The kidney’s capacity to increase filtration above its resting level in response to demand. A normal resting GFR can coexist with reduced capacity to raise filtration when needed.
Estimated glomerular filtration rate: A calculated approximation of glomerular filtration rate based on blood markers and, sometimes, demographic variables. Most reported GFR values are estimates calculated from serum creatinine or cystatin C.
Acute kidney injury: A sudden decline in kidney function, identified by changes in serum creatinine or urine output. Changing filtration can signal acute injury, although creatinine-based estimates lag behind rapid changes.
Glomerulus: A tuft of capillaries in a nephron where blood filtration begins. The combined filtration of functioning glomeruli determines whole-kidney GFR.
Creatinine clearance: An estimate of the volume of plasma cleared of creatinine per unit time, calculated from urine and blood measurements. Creatinine secretion into urine can make its clearance exceed true GFR.
Cystatin C: A protein produced by nucleated cells and filtered by the kidneys, used as a blood marker of filtration. Cystatin C offers an alternative marker when creatinine-based estimates may mislead.
Kidney function tests: Laboratory and clinical assessments used to evaluate how well the kidneys filter and regulate the body. GFR is a central measure within the broader assessment of kidney function.

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