Objective:To explore the clinical characteristics and predictive factors for plastic bronchitis (PB) in children with severe Mycoplasma pneumoniae pneumonia (SMPP). Methods:A retrospective cohort enrolled children with a clinical diagnosis of SMPP who were treated at the Department of Respiratory Medicine of Tianjin Children′s Hospital Machang District from January 1, 2018, to October 31, 2023. According to the bronchoscopy and pathological examination results, the patients were divided into 142 cases in the PB group and 274 cases in the non-PB group. The clinical manifestations, laboratory data, imaging findings, and treatments were analyzed.Mann-Whitney U test and Chi-square test were used to analyze the differences between the two groups, and multivariate Logistic regression was used to analyze the risk factors. The receiver operating characteristic (ROC) curve was used to explore the predictive value of PB in SMPP. Results:Among 416 SMPP children, there were 197 males and 219 females; PB group 142 cases, non-PB group 274 cases, the age of disease onset was (6.9±2.9) years and (6.6±2.8) years in the PB group and the non-PB group respectively. The incidence of wheezing symptoms, hypoxemia, heat peak >40 ℃, the duration of fever, neutrophil-lymphocyte ratio, mean platelet volume, C-reactive protein, procalcitonin, interleukin-6, alanine transaminase, aspartate aminotransferase and ferritin were higher in the PB group (16 cases (11.3%) vs. 15 cases (5.5%), 14 cases (9.9%) vs. 12 cases (4.4%), 57 cases (40.1%) vs. 67 cases (24.5%), 10 (8, 12) vs. 9 (8, 12) d, 6.1 (4.1, 13.1)×10 9vs. 5.0 (3.7, 6.8)×10 9/L, 10.2 (9.6, 10.8) vs. 9.4 (8.9, 10.1) fl, 33.4 (16.0, 67.5) vs. 23.0 (10.4, 56.1) mg/L, 0.24 (0.12, 0.48) vs. 0.16 (0.09, 0.31) μg/L, 39.9 (25.1, 81.4) vs. 31.3 (18.3, 59.3) ng/L, 16.0 (12.0, 29.0) vs. 14.0 (10.0, 24.3) U/L, 38.5 (28.0, 52.5) vs. 33.0 (25.0, 44.0) U/L, 233 (136, 488) vs. 156 (110, 293) μg/L, χ2=4.55, 4.79, 11.00, Z=2.25, 4.00, 6.64, 2.76, 2.98, 3.09, 2.22, 2.62, 4.18, all P<0.05). Multivariate Logistic regression analysis showed that the dyspnea ( OR=2.97, 95% CI 1.35-6.55, P=0.007), the diminution of respiration ( OR=2.40, 95% CI 1.27-4.52, P=0.006), neutrophil-lymphocyte ratio (NLR) ( OR=2.07, 95% CI 1.71-2.51, P<0.001), lactate dehydrogenase (LDH) ( OR=1.01, 95% CI 1.00-1.01, P<0.001), mean platelet volume/platelet count (MPV/PLT) ( OR=1.39, 95% CI 1.13-1.71, P=0.002), pleural effusion ( OR=2.23, 95% CI 1.21-4.13, P=0.011),≥2/3 lobe consolidation ( OR=1.84, 95% CI 1.04-3.00, P=0.039) and atelectasis ( OR=1.98, 95% CI 1.02-3.48, P=0.044) were independent predictors of PB in children with SMPP. ROC curve analysis showed that the cut-off values for NLR, LDH and MPV/PLT in the diagnosis of PB were 2.79 (sensitivity 0.89, specificity 0.69, area under the curve (AUC)=0.86, P<0.001), 474 U/L (sensitivity 0.63, specificity 0.65, AUC=0.70, P=0.003) and 0.04 (sensitivity 0.75, specificity 0.53, AUC=0.68, P=0.005) respectively. Children in the PB group had longer hospital stays and corticosteroid treatment course than those in the non-PB group, the proportion of children in the PB group who received bronchoscopy treatment twice or more was higher (9 (8, 12) vs. 8 (6, 10) d, 7 (5, 8) vs. 6 (5, 7) d, 128 cases (90.1%) vs. 218 cases (79.6%), 106 cases (74.7%) vs. 54 cases (19.7%), Z=6.70, 5.06, χ2=7.48, 119.27, all P<0.05). Conclusions:The dyspnea, respiration diminution, NLR level elevation (>2.79) and pleural effusion were predictive factors for PB in children with SMPP. This provides a basis for the early identification of PB in children with SMPP.