Creatinase (EC 3.5.3.3; abbreviated as CRE) is a hydrolase that catalyzes the hydrolysis of its substrate creatine to produce creatine and urea, and is a key enzyme in creatinine metabolism. CRE is a diagnostic enzyme mainly used for detecting creatinine levels in serum and urine to evaluate renal function. Creatinine is an important metabolic product in the human body, which is mainly filtered by the glomeruli and excreted from the body. A healthy kidney can continuously expel creatinine produced during the metabolic process from the body, thereby maintaining creatinine in the blood within a certain range; If the kidney undergoes pathological changes, creatinine will not be effectively cleared, resulting in its accumulation in the blood. Therefore, measuring the creatinine content in serum and urine is a common biochemical test item in clinical practice, and its content can provide objective indicators for clinical evaluation of glomerular filtration function. The determination methods of creatinine content can be divided into two categories: chemical method and enzymatic method. The chemical method is mainly based on the alkaline picric acid method, but its reaction specificity and sensitivity are poor. Enzymatic method can overcome the shortcomings of the above chemical methods and has the advantages of simple and fast determination methods. Therefore, enzymatic method for determining creatinine content has gradually replaced chemical method. The reaction of enzymatic determination of creatinine content involves a series of transformations of creatinine through CRE coupled creatinase (EC 3.5.2.10) and creatine oxidase (EC 1.5.3.1), ultimately generating H2O2. The content of creatinine in the sample is measured by measuring the amount of H2O2 produced.