| osmolal clearance | The volume of urine that would be excreted per minute if the urinary solutes were accompanied by just enough water to make the urine isosmotic with plasma, i.e., so that the solute excretion did not change the osmolality of body fluids. To calculate it, the volume of urine excreted per minute is multiplied by the urinary osmolality (usually measured by freezing point depression) and divided by the plasma osmolality. Osmolal clearance is less than actual urine flow when urine is hyposmotic and exceeds it when urine is hyperosmotic. (05 Mar 2000) |
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| endogenous creatinine clearance | A term distinguishing measurements based on the creatinine normally present in plasma; since no infusion is necessary, an average value may be obtained by collecting urine for a long period, e.g., 24 hours. (05 Mar 2000) |
| exogenous creatinine clearance | A term distinguishing measurements based on infusing creatinine intravenously to raise its plasma concentration and facilitate its accurate chemical determination. (05 Mar 2000) |
| urea clearance | The volume of plasma (or blood) that would be completely cleared of urea by one minute's excretion of urine; originally calculated as urine flow multiplied by urine urea concentration divided by concentration of urea in whole blood rather than plasma, representing blood urea clearance rather than plasma urea clearance. (05 Mar 2000) |
| urea clearance test | A test of renal function based on urea clearance. (05 Mar 2000) |
| free water clearance | The amount of water excreted in the urine beyond that which would accompany the excreted solutes if the urine were isosmotic with plasma; it represents the loss of body water in excess of solute tending to raise body osmolality and making urine hyposmotic. Unlike other clearance's, it is calculated by subtracting the osmolal clearance from the actual volume of urine excreted per minute. A negative value for free water clearance represents the amount of water that the body has reclaimed from isosmotic tubule fluid to make the urine hyperosmotic and to lower body osmolality. (05 Mar 2000) |