Final answer:
Renal clearance is measured by using the formula Ccr = (U × V) / B, where 'U' is the substance's urine concentration, 'V' is the urine flow rate converted to L/hr, and 'B' is the plasma concentration. For renal plasma flow calculations, blood flow per minute is multiplied by the percentage of plasma (hematocrit subtracted from 100%).
Step-by-step explanation:
Calculating Renal Clearance
To calculate the renal clearance in liters per hour, you need to measure the substance's concentration in the urine (U), the volume of urine excreted per minute (V), and its concentration in the blood plasma (B). The standard formula for creatinine clearance (Ccr) is:
Ccr = (U × V) / B
When expressed in liters per hour, you need to convert the urine flow rate (V) from mL/min to L/hr (1 L = 1000 mL). For instance, if the urine flow rate is 1 mL/min, this translates to 0.060 L/hr after conversion. The same conversion is applied to the clearance which is usually given in mL/min. Multiply the final result by the fraction of an hour (e.g., 30 minutes is 0.5 hours).
The renal plasma flow can be measured using substances like para-aminohippuric acid (PAH) and takes into account the hematocrit to calculate the total blood flow through the kidneys. Example: If blood flow is 1050 mL/min and hematocrit is 45%, then the renal plasma flow is 578 mL/min:
1050 mL/min × 0.55 (since hematocrit is 45%, plasma percentage is 55%) = 578 mL plasma/min