Conversion of creatine and p-creatine to creatinine. Creatine and p-creatine are converted non-enzymatically to the metabolite creatinine, which diffuses into the blood and is excreted by the kidneys. In vivo, this conversion appears to be irreversible and in vitro it is favored by higher temperatures and lower pH. Creatinine forms spontaneously from p-creatine.

Linearity was determined by taking two diluted 1:20 human urine samples, one with a low diluted creatinine level of 0.38 mg/dL and one with a higher diluted level of 9.33 mg/dL and mixing them in the ratios given below. The measured concentrations were compared to the expected values.