A simplified D₃-creatine dilution method for skeletal muscle mass determination with dynamic correction of creatinine and D₃-creatinine using ultra-performance liquid chromatography-tandem mass spectrometry

This study developed a simple method for muscle mass determination based on D-3-creatine dilution by removing the matrix effects of ultra-performance liquid chromatography-tandem mass spectrometry analysis through mutual correction of creatinine and D-3-creatinine. Rats were administered an oral tracer dose of D-3-creatine at age 6 weeks. Creatinine and D-3-creatinine in urine were detected using ultra-performance liquid chromatography-tandem mass spectrometry after diluting 20 times to obtain D-3-creatinine enrichment factor (mole percent excess). The mole percent excess obtained from peak area could be used to calculate muscle mass using the improved formula. The limit of detection was 0.500 ng/mL for D-3-creatinine. Creatinine and D-3-creatinine could be mutually corrected because of the same matrix effect, and D-3-creatine spillage was negligible within 0.22%. Isotopic steady time was consistent with that obtained using conventional methods. Bland-Altman plots demonstrated the satisfying consistency between the proposed method and magnetic resonance imaging. This is a simple and rapid measuring method of muscle mass based on D-3-creatine dilution that requires no accurate quantification of creatinine and D-3-creatinine concentrations and no urine sample collection to obtain D-3-creatine spillage.