The value of blood creatinine has a great relationship with kidney function, and it is an important observation indicator of whether kidney function has changed. Creatinine is the product of metabolism of all muscle systems in the human body, and when the daily activity of the human body is relatively constant and does not participate in strenuous physical exercise, the daily amount of creatinine produced is basically more constant. If a person with normal kidney function has a blood creatinine value, it will be within a relatively normal range. When the excretory function of the kidneys decreases and creatinine excretion from the urine decreases, the creatinine concentration in the blood will be found to be significantly higher during the test, which indicates a change in kidney function in such patients. Unlike urea nitrogen, which is also an indicator of kidney function, creatinine is a relatively constant indicator of kidney function, as it is disturbed by inflammation, high protein diet, gastrointestinal bleeding and other changes in the internal environment. Therefore, to see whether the kidney function of the patient is changed, the main tests are blood creatinine and urea nitrogen, of which blood creatinine is the main indicator.