The compensatory function of the kidneys is very strong. In normal people, as long as one of the two kidneys is functioning, the blood creatinine can be maintained at a normal level. In other words, kidney function must decline to a certain degree before it will cause an increase in blood creatinine in the clinical so-called “kidney function” test. Therefore, blood creatinine does not reflect early, mild renal function loss. Creatinine is produced by muscle metabolism, and its production is closely related to the degree of muscle metabolism and the amount of muscle. People who have a large amount of muscle in their body will have a large amount of creatinine production; people who have a small amount of muscle will have a relatively small amount of creatinine production. Women have less muscle than men, so under normal circumstances, women’s blood creatinine levels are about 15% lower than those of men. As we age, the total amount of muscle in the body gradually decreases, and the absolute level of blood creatinine decreases. Normally, the blood creatinine level decreases by about 1% per year after the age of 40, which means that the normal value of blood creatinine in older people will be lower than that of younger people. In addition, patients with chronic diseases such as diabetes, tumors and people who are more emaciated will also have lower blood creatinine reference values because they have less muscle mass. Therefore, when you get the kidney function test report and see your blood creatinine value, you should also calculate the glomerular filtration rate in combination with your gender, age and weight to get an accurate picture of your kidney function.