MEDizzy - The following laboratory values were obtained in a

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The Body Fluids and Kidneys (I)

The following laboratory values were obtained in a 58-year-old man: Urine volume : 4320 milliliters of urine collected during the preceding 24 hours Plasma creatinine : 3 mg/100 ml Urine creatinine : 50 mg/100 ml Plasma potassium : 4.0 mmol/L Urine potassium : 30 mmol/L What is his approximate GFR, assuming that he collected all of his urine in the 24-hour period?

ExplanationGFR is approximately equal to creatinine clearance, which is calculated as the urine creatinine concentration (50 mg/100 ml) × urine flow rate (3 ml/min)/plasma creatinine concentration (3 mg/100 ml), which is equal to 50 ml/min. Urine flow rate = 4320 ml/24 h = 4320 ml/1440 min = 3 ml/min.