目的 分析中性粒细胞胞外诱捕网（NETs）标记物游离DNA（cf-DNA）在肺炎支原体肺炎（MPP）患儿体内的表达水平，探讨cf-DNA/NETs对MPP患儿病情严重程度的预测效能。 方法 前瞻性选取115例MPP患儿作为MPP组，根据病情严重程度，将MPP组分为轻症组（n = 75）和重症组（n = 40）。同期随机选取50例健康体检儿童作为对照组。检测MPP组及对照组血清cf-DNA水平及MPP组C反应蛋白（CRP）、D-二聚体、乳酸脱氢酶（LDH）、白介素-6（IL-6）、γ干扰素（IFN-γ）及肿瘤坏死因子-α（TNF-α）水平，比较各组血清cf-DNA及相关炎症因子的水平差异，并分析血清cf-DNA在评估MPP病情严重程度中的作用。 结果 MPP组患儿血清cf-DNA水平较对照组明显升高，且在重症组升高更显著（P < 0.05）。重症组CRP、D-二聚体、LDH、IL-6、IFN-γ及TNF-α水平均高于轻症组（P < 0.05）。多因素logistic回归分析发现血清cf-DNA、CRP及IL-6水平升高与MPP病情严重程度密切相关（P < 0.05）。受试者操作特征曲线分析结果显示血清cf-DNA、CRP及IL-6三者联合预测重症MPP的曲线下面积为0.981，高于各指标单独预测（P < 0.05）。 结论 血清cf-DNA/NETs与MPP患儿病情严重程度密切相关，cf-DNA、CRP及IL-6三者联合检测更有利于判断MPP患儿的病情严重程度。

Objective The aim of this study is to analyze the expression level of cell-free DNA （cf-DNA）， a biomarker of neutrophil extracellular traps （NETs）， in children with Mycoplasma pneumoniae pneumonia （MPP）， and to explore the predictive efficacy of cf-DNA （as a marker of NETs） for the severity of MPP in these children. Methods A total of 115 children with MPP were prospectively selected as the MPP group. Based on the disease severity， the MPP group was categorized into the mild group （n = 75） and the severe group （n = 40）. During the same period， 50 healthy children undergoing physical examinations were selected as the control group. The levels of serum cf-DNA in the MPP group and the control group， as well as the levels of C-reactive protein （CRP）， D-dimer， lactate dehydrogenase （LDH）， interleukin-6 （IL-6）， interferon-γ （IFN-γ）， and tumor necrosis factor-α （TNF-α） in the MPP group were detected. The differences in the levels of serum cf-DNA and related inflammatory factors among the groups were compared， and the role of serum cf-DNA in evaluating the severity of MPP was analyzed. Results The level of serum cf-DNA in children of the MPP group was notably higher than that in the control group， with a more significant elevation observed in the severe group （P < 0.05）. The levels of CRP， D-dimer， LDH， IL-6， IFN-γ， and TNF-α were all higher in the severe group than in the mild group （P < 0.05）. Multivariate logistic regression analysis showed that the increased levels of serum cf-DNA， CRP， and IL-6 were closely related to the severity of MPP （P < 0.05）. The results of receiver operating characteristic （ROC） curve analysis showed that the area under the curve （AUC） of the combination of serum cf-DNA， CRP， and IL-6 for predicting severe MPP was 0.981， which was higher than that of each index alone （P < 0.05）. Conclusions Serum cf-DNA （as a marker of NETs） is closely related to the severity of MPP in children. The combined detection of cf-DNA， CRP， and IL-6 is more beneficial for assessing the severity of MPP in children.