Abstract: Objective To analyze the detection and assessment value of serum lactate dehydrogenase (LDH) in children with Mycoplasma pneumoniae pneumonia(MPP), and to explore the threshold of LDH in MPP children with different clinical features/disease indications. Methods Totally 257 children with MPP who were hospitalized in Huai′an Hospital from February 2020 to July 2023 were selected as the case(test) group and 257 healthy children who underwent physical examinations in the outpatient department of Huai′an Hospital in same period were selected as the control group. Serum LDH level of two groups before and after treatment were compared and analyzed. According to the severity of MPP in children, they were divided into ordinary MPP and severe MPP. The medical records of MPP patients were collected. The serum LDH levels of children with different clinical characteristics were analyzed, and the diagnostic/predictive evaluation value and threshold of serum LDH under different clinical characteristics/disease indications were explored by receiver operation characteristic (ROC). Results 1)The serum LDH level gradually increased in control group, normal MPP group and severe MPP group(P＜0.05); 2)The group of children with respiratory virus mixed infection, lung lesions accounting for≥1/3 of the total lung volume, post-infections bronchiolitis obliterans(PIBO), pleural effusion, and extra-pulmonary complications showed a significantly higher serum LDH level compared to the group of children without these conditions or with negative corresponding indicators (P＜0.05).3)On the first day of admission, there was a positive correlation between serum LDH level and the total duration of fever in MPP patients (P＜0.001); 4)ROC analysis showed that serum LDH level had an impact on respiratory virus coinfection, pneumonia severity PIBO, The ROC-AUC (95% CI) of detection and assessment values for the diagnostic indicators of pleural effusion and extra-pulmonary complications were 0.723 (0.456-0.970), 0.772 (0.563-0.966), 0.699 (0.401-0.980), 0.750 (0.502-0.981), and 0.725 (0.507-0.927),respectively. The highest was the detection evaluation of pneumonia severity, and the lowest was the detection evaluation of PIBO. The corresponding detection evaluation thresholds (U/L) were 860, 880, 850, 830, and 900, respectively; The predictive value of serum LDH levels for the severity of MPP in children: ROC-AUC (95% CI) was 0.777 (0.636-0.920), corresponding to a predictive evaluation threshold (U/L) of 760. Conclusions Serum LDH is closely related with respiratory virus co-infection and severe pneumonia shown by chest X-rays in children with MPP PIBO. Elevated level of serum LDH is observed in cases of pleural effusion, extra-pulmonary complications and severe illness. LDH may support diagnosis or prediction of clinical course and indications of MPP in children.

Key words: lactate dehydrogenase, Mycoplasma pneumoniae pneumonia, children, extra pulmonary complications