In the creatinine clearance calculation example, the plasma creatinine concentration was which value?

• A. 0.2 mg/dL
• B. 0.6 mg/dL
• C. 1.2 mg/dL
• D. 2.4 mg/dL

Answer: (C)

Creatinine clearance uses the formula Ccr = (Ucr × V) / Pcr, so the plasma creatinine concentration is the value in the denominator that determines the final clearance. In the example, the numbers are plugged in with Pcr equal to 1.2 mg/dL. This keeps the calculated clearance within a plausible range for the scenario. If the plasma concentration were 0.2 mg/dL or 0.6 mg/dL, the same urine creatinine and urine flow would yield a noticeably higher clearance, suggesting a faster filtration rate than the data support. If it were 2.4 mg/dL, the clearance would be much lower, implying severe impairment inconsistent with the given values. Therefore, the plasma creatinine concentration used is 1.2 mg/dL.