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What is the glomerular filtration rate (GFR)?

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All blood in the body flows through the kidneys hundreds of times each day. The kidneys push the liquid part of blood through tiny filters (called nephrons), then reabsorb most of the fluid back into the blood. The fluid and waste products that the kidneys don't reabsorb are excreted as urine.

The rate of blood flow through the kidneys is the glomerular filtration rate, or GFR. (The glomeruli are microscopic bundles of blood vessels inside nephrons, and are crucial parts of the filtering system.) The glomerular filtration rate can't be measured directly -- that's where measuring creatinine and creatinine clearance comes in.

SOURCES: Brenner, B. Saunders Elsevier, 2007.  National Kidney Foundation web site: "Chronic Kidney Disease."

Brenner & Rector's The Kidney, 8th Edition,

National Kidney Foundation web site: "Key Points: Living With Stage 4 Kidney Disease."

Johns Hopkins Medicine web site: "Health Library: 24-Hour Urine Collection."

Family Practice Notebook web site: "Creatinine Clearance."

UpToDate.com literature review: "Reciprocal serum creatinine concentration and chronic kidney disease" and "Definition and staging of chronic kidney disease in adults."

Reviewed by Melinda Ratini on October 22, 2017

SOURCES: Brenner, B. Saunders Elsevier, 2007.  National Kidney Foundation web site: "Chronic Kidney Disease."

Brenner & Rector's The Kidney, 8th Edition,

National Kidney Foundation web site: "Key Points: Living With Stage 4 Kidney Disease."

Johns Hopkins Medicine web site: "Health Library: 24-Hour Urine Collection."

Family Practice Notebook web site: "Creatinine Clearance."

UpToDate.com literature review: "Reciprocal serum creatinine concentration and chronic kidney disease" and "Definition and staging of chronic kidney disease in adults."

Reviewed by Melinda Ratini on October 22, 2017

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