Sat27November0556PM 6

A patient has a plasma creatinine concentration of 10 mcg/ml and over a four hour period produces 240 ml of urine. The urinary concentration of creatinine is 1.25 mg/ml.

What is the approximate creatinine clearance of this patient?

(Please select 1 option)

12.5 ml/minute

1.25 ml/minute Incorrect answer selected

240 ml/minute

125 ml/minute This is the correct answer

24 ml/minute

Explanation

Clearance (CL)

U = urinary creatinine concentration (mg/ml)

V = volume of urine ml/minute

P = plasma creatinine concentration (mg/ml).

Mathematically:

CL= U.V/P

CL = 1.25 mg/ml x 1 ml/minute = 125 ml/minute

                0.01 mg/ml

Clearance can be defined as the volume of blood or plasma which is completely cleared of drug per unit time. The symbol is CL and the units are ml/min.

Creatinine is an endogenous substance which is primarily filtered or reabsorbed from the kidney but is secreted in very small amounts (unlike inulin). Therefore, it can readily be used as an estimate of glomerular filtration rate.

Creatinine clearance (CLcr) as an indicator of renal filtration, will parallel any changes in secretion and reabsorption. Therefore, CLcr can be used as an overall estimate of renal function. Creatinine clearance often overestimates actual glomerular filtration rate by 10- 20% because of active secretion in the peritubular capillaries.

The gold standard for the measurment of GFR is inulin.

Answer Statistics

1

18%

2

19%

3

3%

4

49%

5

14%

Times answered: 250