Filtering the blood

Clinically: Glomerular filtration

What normal looks like

Healthy adult kidneys filter roughly 90 to 120 mL of plasma per minute, processing the body's entire blood volume many times a day. Filtration declines gradually with age, and a modest decline in an older adult is expected rather than alarming.

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

function unverified

Each kidney holds about a million tiny filters. They let water, salt and waste through while holding back blood cells and most proteins. How fast they work is the main thing a kidney blood test is measuring.

The glomerulus filters by size and charge, retaining albumin and cells while passing water, electrolytes and small solutes. Filtration rate is the single most useful summary of renal function, which is why eGFR is reported.

In clinical terms

Passive ultrafiltration of plasma across the glomerular capillary wall, producing the filtrate that the tubule then modifies.