Glomerular filtration rate
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Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal glomerular capillaries into Bowman's capsule per unit time. Clinically, this is often measured to determine renal function.
The GFR was originally determined by injecting inulin (not insulin) into the plasma. Since inulin is not reabsorbed by the kidney after glomerular filtration, its rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. In clinical practise however, creatinine clearance is used to measure GFR. Creatinine is an endogenous molecule, synthesized in the body, which is freely filtered by the glomerulus (but also secreted by the renal tubules in very small amounts). Creatinine clearance is therefore a close approximation of the GFR. The GFR is typically recorded in milliliters per minute (ml/min).
Example: A person has an plasma creatinine concentration of 0.01 mg/ml and in 1 hour he excretes 75 mg of creatinine in the urine. The GFR is calculated as M/P (where M is the mass of creatinine excreted per unit time and P is the plasma concentration of creatinine). <math>GFR = \frac{\frac{75mg}{60mins}}{0.01mg/ml} = 125 ml/min<math>
The normal range of GFR for males and females is: Male: 97 to 137 ml/min. Female: 88 to 128 ml/min.
External links
- Glomerular Filtration Rate (http://www.fpnotebook.com/REN70.htm) - FP Notebook.
- Learn about your GFR and other lab values (http://www.kidney.org/kls/public/knowGFR.cfm) - US Kidney Foundation.
- Creatinine Clearance (http://health.allrefer.com/health/creatinine-clearance-values.html) - The normal ranges of GFR.