Renal function tests require patients to have blood drawn on an empty stomach for the indicators obtained. The kidney function test mainly includes blood creatinine, urea nitrogen and uric acid, the three basic tests. In addition, if more items are done, it may also include cystatin C, albumin, blood β2 microglobulin and other tests. The specific meaning of each test: First, blood creatinine, creatinine is a small molecule toxin produced by muscle metabolism, which is filtered through the glomerulus and excreted in the form of urine. If there is a problem with the kidney function, the blood creatinine will be increased accordingly. Secondly, urea nitrogen, which is excreted from urine through glomerular filtration, is a small molecule toxin produced by human protein decomposition and metabolism. Elevated urea nitrogen is common in patients with renal insufficiency, and may also be seen in patients with high protein diet, as well as in patients with inadequate renal perfusion, such as patients with gastrointestinal hemorrhage and dehydration. Thirdly, uric acid, excreted through the kidneys, so when there is a problem with kidney function, there is a corresponding increase in uric acid, similar to patients with gout, who also have elevated uric acid.