The main purpose of the five renal function tests is to rule out the presence of renal failure, whether uric acid is elevated, and whether there is malnutrition. The more important items in the five renal function tests are urea, creatinine, cystatin C and uric acid, and another item is the ratio of urea to creatinine. If urea and creatinine are found to be elevated, it indicates that the patient has renal failure. Renal failure is more serious, which indicates that the kidney’s detoxification ability is reduced and the next step may develop into uremia, so it should be taken seriously. Elevated uric acid does not necessarily mean kidney failure, but elevated uric acid can cause not only gout, but also deterioration of kidney function, such as uric acid nephropathy is one of the very important causes of kidney failure. Another is the presence of cystatin C, which can detect early kidney disease. If urea, creatinine and uric acid are not increased but decreased, and the decrease is more obvious, this situation indicates that the patient may be malnourished, too strict control of the diet, and need to supplement nutrition.