Creatinine is formed from which precursor?

Creatinine is formed from which precursor?

• A. Urea
• B. Glucose
• C. Creatine
• D. Uric acid

Answer: (C)

Creatinine is formed from creatine. In muscle, creatine (and its phosphorylated form, phosphocreatine) slowly undergoes a non-enzymatic cyclization to creatinine, which then enters the bloodstream and is filtered out by the kidneys. The rate of creatinine formation is fairly steady and largely reflects muscle mass, which is why serum or urine creatinine levels are used to assess kidney function. Urea, uric acid, and glucose are not direct precursors to creatinine—urea comes from amino acid breakdown via the urea cycle, uric acid from purine degradation, and glucose is a simple sugar without a direct path to creatinine.

Creatinine is formed from creatine. In muscle, creatine (and its phosphorylated form, phosphocreatine) slowly undergoes a non-enzymatic cyclization to creatinine, which then enters the bloodstream and is filtered out by the kidneys. The rate of creatinine formation is fairly steady and largely reflects muscle mass, which is why serum or urine creatinine levels are used to assess kidney function. Urea, uric acid, and glucose are not direct precursors to creatinine—urea comes from amino acid breakdown via the urea cycle, uric acid from purine degradation, and glucose is a simple sugar without a direct path to creatinine.