Linearity was determined by taking two human serum samples, one with a low diluted creatinine level of 0.58 mg/dL and one with a higher level of 1.23 mg/dL and mixing them in given ratios. The measured concentrations were compared to the expected values.

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 pH2. Creatinine forms spontaneously from p-creatine.