Sepsis is a serious systemic infection caused by pathogenic microorganisms that enter the blood circulation, grow and multiply in the blood environment and produce toxins. The diagnosis is based on two main aspects, on the one hand, the symptoms exhibited by the body, and on the other hand, the various tests as an auxiliary diagnostic tool. Specific tests include routine blood tests, routine urine tests, bacterial culture of secretions + drug sensitivity tests, imaging tests, etc. Among them, the most important tests are routine blood tests, bacterial culture + drug sensitivity, and neutrophil tetrazolium blue test. The abnormal results of routine blood tests in patients with sepsis may be indicated by a significant increase in the total white blood cell count, which can be as high as 10×109/L, and a significant increase in the percentage of neutrophils, mostly above 80%, as well as the detection of toxic granules and leftward nuclear shift. However, there are exceptions, for example, in immunocompromised individuals and in patients with gram-negative sepsis, the results of routine blood tests may show no increase in total leukocyte count. Routine urine tests may suggest proteinuria, positive urinary ketone bodies, and also red blood cells in the urine. In cases with concomitant urinary tract infection, purulent hematuria may be found in the urine. Smear examination of blood, bone marrow, primary lesions, and purulent secretions from migratory lesions is performed. Blood and bone marrow can be cultured plus drug sensitivity to facilitate clarification of the pathogenic bacteria, which is helpful in guiding the physician’s medication and selecting drugs with strong therapeutic effects. Depending on the site of infection, other tests may also be performed. For example, if the sepsis is caused by lung infection, imaging tests such as X-ray, chest CT, etc. can be supplemented. If the sepsis is caused by an infection in the liver or biliary tract, ultrasound may be chosen to assist in the diagnosis. If the source of infection of sepsis cannot be found, other tests can be further taken, such as molecular biology tests that can be perfected: gene chip, polymerase chain reaction, etc.