False Statement About Creatinine

Which statement is NOT true about creatinine?

Correct Answer: Creatinine production depends on the amount of protein metabolism

This is NOT true. Creatinine production depends on muscle mass, NOT on the amount of protein metabolism.

Correct Facts About Creatinine

• Source: Creatinine is a breakdown product of creatine phosphate (phosphocreatine) in skeletal muscles — a byproduct of muscle energy metabolism
• Production rate: Depends on total muscle mass — an athlete with more muscle mass produces more creatinine than a sedentary person of the same weight
• Daily production is relatively constant in an individual (because muscle mass is stable)
• Creatinine is freely filtered at glomerulus and NOT significantly reabsorbed

What Depends on Protein Metabolism?

It is urea (BUN - Blood Urea Nitrogen) production that depends on protein metabolism. Protein → amino acids → deamination → NH₃ → liver converts NH₃ to urea via urea cycle → excreted in urine.

Why Other Statements Are TRUE

• Nitrogenous byproduct of muscle metabolism — TRUE (creatine phosphate → creatinine)
• High plasma creatinine = first indication of kidney disease — TRUE (accumulated when GFR drops)
• Creatinine clearance = measure of GFR — TRUE (gold standard alongside inulin clearance)