A nutrition researcher wishes to estimate the skeletal muscle mass of a healthy adult non-vegetarian subject over a stable diet. Which measurement provides the most reliable indirect index of total muscle mass?
- A 24-hour urinary creatinine excretion ✓
- B 24-hour urinary uric acid excretion
- C 24-hour urinary urea nitrogen excretion
- D Serum creatine phosphokinase level
Correct answer: A. 24-hour urinary creatinine excretion
Explanation
Creatine is phosphorylated to creatine phosphate in skeletal muscle and spontaneously cyclises at a constant daily rate of about 1 to 2 percent of the total body creatine pool to form creatinine, which is excreted quantitatively in urine. Because virtually all body creatine resides in muscle, steady-state 24-hour urinary creatinine output correlates closely with total skeletal muscle mass. Uric acid reflects nucleoprotein turnover, urea nitrogen reflects total protein catabolism including dietary intake, and serum CK varies with membrane injury rather than mass.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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