Creatinine is a kind of metabolic waste in human body, which is mainly excreted by kidneys. The daily production and excretion are relatively constant, and the influence of diet and drinking water is very small, therefore, fasting is not required to check kidney function. For the evaluation of kidney diseases, besides checking kidney function, urine routine and kidney ultrasound are also required to understand whether there are kidney diseases. Kidney-related diseases commonly include nephritis, nephrotic syndrome, diabetic nephropathy, etc. They need to be treated actively in the early stage of these diseases to avoid deterioration, and once the kidney disease develops to the final stage, which is the uremic phase, dialysis treatment needs to be started.