A patient showing symptoms of impaired renal function has a battery of tests performed.Results are:
Serum creatinine: 2.0 mg/dL
Urine creatinine: 150 mg/dL
Serum osmolality: 270 mOsm
Urine osmolality: 100 mOsm
24-hour urine volume: 2000 mL
-Based on the information provided,calculate the free water clearance.
A) -0.5
B) -1.0
C) +0.6
D) +0.9

Question

Quizplus · Accepted Answer

Free water clearance (C_H2O) is calculated using the formula: C_H2O = V - C_Osm, where V is urine flow rate and C_Osm is osmolar clearance. C_Osm = (U_osm * V) / P_osm. Here, V = 2000 mL/24hr = 83.33 mL/hr, U_osm = 100 mOsm, P_osm = 270 mOsm. C_Osm = (100 * 83.33) / 270 = 30.86 mL/hr. C_H2O = 83.33 - 30.86 = 52.47 mL/hr. Converting to L/day: 52.47 mL/hr * 24 hr = 1.26 L/day. The closest choice is +0.9.

A Patient Showing Symptoms of Impaired Renal Function Has a Battery