Flaccid fever, also known as septic fever, is commonly seen in clinical practice as a routine blood test. Routine blood test is the most general and basic blood test. Routine blood tests are usually taken from peripheral blood for examination, such as blood from the fingertip or earlobe area. After passing through the blood cell analysis instrument, the computer reports the results and this item has become a routine for examining patients. Blood consists of two major parts, liquid and tangible cells, and the routine blood test is the cellular part of blood. 1.Blood picture: half of the white blood cells are normal or mildly reduced, and the lymphocytes are relatively or absolutely increased, and the classification can be more than 60%. Blood sedimentation increases rapidly in all phases. 2, bacteriological examination: patients’ blood, bone marrow, breast milk, uterine secretions can be done for bacterial culture. The positive rate is high in the acute phase and low in the chronic phase. Bone marrow specimens have a higher positive rate than blood specimens. 3. Immunological examination: (1) Serum agglutination test. (2) Complement binding test. (3) Anti-human globulin test. (4) Enzyme-linked immunosorbent assay.