Creatinine: Activity Assays

Creatinine is a non-enzymatic metabolite of phospho-Creatine, a molecule used primarily by muscle tissue as a store for high-energy phosphate that can be utilized for the production of ATP. Creatinine diffuses into the blood and is excreted by the kidneys at a relatively constant rate. Creatinine levels in the urine are used as a measurement of renal function.