3. A man’s leg was crushed between a car bumper and a wall. His physicians belie
ID: 3477042 • Letter: 3
Question
3. A man’s leg was crushed between a car bumper and a wall. His physicians believe their patient has suffered kidney damage from myoglobin blocking glomerular pores. Tests showed the following results:
Plasma creatinine 38.7 mg/dL plasma
24 hr urine specimen volume = 1 liter
Urine creatinine 293 mg/dL urine
A. How many mg of creatinine are in the urine specimen? How much creatinine appears in the urine per hour?
B. What is the patient’s creatinine clearance in mL/min?
C. What is the patient’s GFR?
D. Is this a normal GFR? Did the patient likely sustain kidney damage?
Explanation / Answer
1. 1dL=0.1 L
Urine has 293 mg/dL
Urine will have 293/0.1=29.3 mg in entire 24 hours specimen (1L volume)
293 mg were present in 24 hours. Hence, 293/24=12.21 mg/dl per hours or 1.221 mg/L per hour
2. Creatinine clearance=CrCl = UCr * UVol/PCr * Tmin
UCr= Urine creatinine (mg/dL)
UVol= volume of urine collected (ml)
PCr=Plasma creatinine (mg/dL)
Tmin= Sample collection time in min
Creatinine clearance= 293 X 1000/38.7 X 24 X60= 5.27 mL/min
3. GFR X PA=V X UA
PA= plasma creatinie concentration mg/mL= 293/100 ml= 2/93 mg/ml
UA=urine creatinine concentration mg/mL= 38.7 mg/100 ml=0.387 mg/ml
V=volume in ml/min
In 24 hrs, 1L was collected.
Hence, in 1 min, 1000ml/24X60=0.695 ml/min
GFR= V X UA/PA= 0.695 X 2.93 mg/mL/0.387 mg/mL= 5.26 ml/min
We need to consider
GFR= 5.26 mL/min
GFR= 5.26 ml/min/1.73 m2=3.044 mL/min/1.73m2 (for standard age and weight)
As this level is lower than 15 mL/min/1.73m2, the patient is suffering from kidney failure.
4. Normal GFR levels are 90-120 mL/min/1.73 m2. As patient’s level is lower than 15 mL/min/1.73m2, the patient is suffering from kidney failure.
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