White blood cell counts are mostly increased or may show a decrease. Neutrophils are mostly elevated. Bacterial culture specimens may be obtained from blood, cerebrospinal fluid, urine, etc. The significance of sputum culture is still controversial. The value of drug sensitivity testing should be emphasized. In molecular epidemiology there are PFGE, RAPD, 16S rRNA gene sequencing and other methods each have their advantages and disadvantages. 1, blood routine: leukocyte count and neutrophil count are significantly increased, and there may be left shift of nucleus. However, the leukocyte count may not be high in immunocompromised individuals with low body response or in elderly and pediatric patients. 2. Urine routine: In urinary tract infection, the urine is cloudy, with leukocytes >5/HP, and may be accompanied by red blood cells, urine protein and tubular pattern, etc. (1) Bacterial culture: Positive blood culture and bone marrow culture are the main basis for confirming the diagnosis, and the latter has a higher positive rate. In order to obtain a higher positive rate, specimens should be collected before the use of antibiotics and chills and high fever as much as possible, repeatedly sent for examination, each time to collect 5-10 ml of blood. for patients who have been treated with antibiotics, the time of blood collection should avoid the peak time of antibiotics in the blood, or add appropriate antibiotic-destroying drugs such as penicillinase, magnesium sulfate in the culture medium or do blood clot culture, in order to improve the positive rate of blood culture. Sputum must be inoculated and cultured within 10 min after collection, and the same bacteria should be cultured several times, or quantitative sputum culture will have greater clinical diagnostic significance. Before inoculating sputum specimens for culture, it is best to examine the sputum specimens microscopically for white blood cell count and squamous epithelial cell count to determine whether the sputum specimens are qualified. In order to avoid contamination of the oral cavity with resident bacteria, sputum can be aspirated from the trachea, or aspirated from the lower respiratory tract with a fibrinoscope through an anti-pollution brush for bacterial culture. Other body fluid cultures include urine from patients with urinary tract infections, cerebrospinal fluid from patients with meningitis, or secretions from other infected sites. When the bacterial culture is positive, it is appropriate to conduct the relevant antibiotic sensitivity test for the selection of appropriate antibacterial drugs for treatment. (2) Bacterial smear: direct smear examination of pus, cerebrospinal fluid, pleural fluid, ascites, petechiae, etc. can also detect pathogenic bacteria, which has a certain reference value for rapid diagnosis. 4, other tests: Limulus lysate test (LLT) is to determine the endotoxin in each body fluid by using the principle that the coagulable protein in the lysate of horseshoe crab cells can form a gel in the presence of endotoxin, and it helps the diagnosis of Gram-negative bacillus sepsis when it is positive. Patients with pulmonary infections can be seen as lamellar or patchy shadows on chest x-ray. With the promotion of molecular biology in clinical practice, genetic diagnostic techniques will greatly improve the positive rate of specimens and determine the presence of drug-resistant genes. Patients with pulmonary infections may have lamellar or patchy shadows on chest X-ray.