Abstract: Objective To explore the early diagnostic value of the classification of peripheral blood leukocytes and the levels of Calcitonin (PCT), C-reaction protein (CRP), and Mycoplasma pneumoniae antibody in children with Mycoplasma pneumoniae complicated with bacterial infectious pneumonia. Methods 500 children with Mycoplasma pneumoniae complicated with bacterial pneumonia who received treatment at the Changping District Integrated Traditional Chinese and Western Medicine Hospital in Beijing from July 2020 to March 2023 were selected as the research group, and 100 children with viral pneumonia who received treatment at the same time at the Changping District Integrated Traditional Chinese and Western Medicine Hospital in Beijing were selected as the case control group. 100 healthy children who underwent physical examination at the same time were selected as the control group, and their blood samples were tested for PCT, CRP, and The levels of Mycoplasma pneumoniae antibody IgM and peripheral blood leukocyte classification indicators (white blood cell count, neutrophil percentage, lymphocyte percentage, monocyte percentage) were compared between the two groups of children. The diagnostic value of the above indicators for Mycoplasma pneumoniae combined with bacterial infection pneumonia was calculated by drawing receiver operating characteristics (ROC) of the subjects, And calculate the area under curve (AUC). Results The blood PCR, CRP, and IgM levels of Mycoplasma pneumoniae antibodies in the study group were significantly higher than those in the case control group and control group children (P<0.05).The peripheral blood white blood cell count, neutrophil percentage, and monocyte percentage of children in the study group were significantly higher than those in the case control group and control group, while the lymphocyte percentage was significantly lower than those in the control group (P<0.05). By plotting ROC curves and calculating, it was found that the diagnostic AUCs for PCT, CRP, and IgM antibodies against Mycoplasma pneumoniae combined with bacterial pneumonia were 0.934 (95%CI=0.900-0.968, P<0.001), 0.928 (95%CI=0.880-0.975, P<0.001), and 0.780 (95%CI=0.712-0.848, P<0.001). The diagnostic AUCs of white blood cell count, neutrophil percentage, lymphocyte percentage, and monocyte percentage in peripheral blood white blood cell classification for Mycoplasma pneumoniae complicated with bacterial infection pneumonia were 0.957 (95%CI=0.925-0.988, P<0.001), 0.768 (95%CI=0.700-0.836, P<0.001), 0.670 (95% CI=0.595-0.746, P<0.001), and 0.765 (95%CI=0.698-0.832, P<0.001). Conclusion The blood PCT, CRP, and IgM of Mycoplasma pneumoniae antibodies in children with Mycoplasma pneumoniae combined with bacterial infection pneumonia significantly increased compared to healthy children, and the level of white blood cell classification also showed significant changes. The above indicators have good application value in the early diagnosis of Mycoplasma pneumoniae combined with bacterial infection pneumonia in children.

Key words: classification of peripheral blood leukocytes, calcitonin, C-reactive protein, antibodies against Mycoplasma pneumoniae, Mycoplasma pneumoniae combined with bacterial infection pneumonia, early diagnostic effectiveness