clearance
Summary
Clearance is the volume of plasma from which a substance is completely removed by an organ per unit time, typically expressed in mL/min. It's a fundamental concept in pharmacokinetics and renal physiology, with creatinine clearance being the gold standard for assessing kidney function.
Detail
Clearance represents the efficiency of an organ (usually kidneys or liver) in eliminating a substance from the body. Mathematically, clearance = (U × V)/P, where U is urine concentration, V is urine flow rate, and P is plasma concentration. Renal clearance involves three processes: glomerular filtration, tubular secretion, and tubular reabsorption. Creatinine clearance approximates GFR since creatinine is freely filtered but neither secreted nor reabsorbed significantly. Normal creatinine clearance is ~120-130 mL/min in healthy adults. Inulin clearance provides the most accurate GFR measurement as it's only filtered. PAH (para-aminohippuric acid) clearance measures renal plasma flow since it's both filtered and secreted. Hepatic clearance determines drug metabolism rates and is crucial for dosing medications. Clearance concepts are essential for understanding drug kinetics, renal function assessment, and therapeutic drug monitoring.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Goodman & Gilman's Pharmacological Basis of Therapeutics
- Brenner & Rector's The Kidney
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.