Factors influencing the production of creatinine: implications for the determination and interpretation of urinary creatinine and creatine in man.
Level 5 - mechanism / opinion, no new human data
In vitro chemical kinetics and ex vivo laboratory storage study
PubMed 3416481 · doi:10.1016/0009-8981(88)90096-4
What was done
Authors measured the rates and equilibrium of creatine and creatinine inter-conversions under controlled temperature and pH simulating urine storage. Creatine and creatinine concentrations and ratios were measured in standard solutions and in urine samples from patients with various pathophysiological conditions before and after storage.
What was found
Reaction rates increased with temperature. The conversion of creatine to creatinine reached a maximum rate around pH 3.7, while the reverse conversion (creatinine to creatine) peaked around pH 5.0. Low pH shifted equilibrium toward creatinine, whereas above approximately pH 6.0, equilibrium resulted in roughly equimolar quantities of both compounds. Baseline urinary creatine ranged from virtually nil to approximately double the creatinine concentration and changed during storage in line with model predictions.
Why it matters
Because temperature and pH cause spontaneous inter-conversion of creatine and creatinine during storage, unstandardized pre-analytical handling can distort clinical evaluations of muscle mass, nutritional status, and 24-hour urine collection completeness.
Limits
The abstract omits the number of human participants, clinical diagnoses, exact temperatures tested, specific storage durations, and precision metrics or confidence intervals.
Cited by
- contradicts Creatine does not degrade into creatinine in warm liquid unless superheated for a prolonged period.