OBJECTIVETo investigate the changes in serum YKL-40 level and humoral immune function and their significance in children with recurrent pneumonia.

METHODSBlood samples were collected from 30 children with recurrent pneumonia (recurrent pneumonia group), 30 children with acute pneumonia (acute pneumonia group), and 30 healthy children (control group). Serum YKL-40 levels were measured by enzyme-linked immunosorbent assay. The correlation between serum YKL-40 level and laboratory indices related to humoral immune function was analyzed. The receiver operating characteristic (ROC) curve was used to analyze the diagnostic value of serum YKL-40 level for recurrent pneumonia.

RESULTSThe recurrent pneumonia group had a significantly higher serum YKL-40 level than the acute pneumonia and control groups (P<0.05). The acute pneumonia group had a significantly higher serum YKL-40 level than the control group (P<0.05). Serum levels of IgG and complement 4 in the recurrent pneumonia group were significantly lower than in the acute pneumonia group (P<0.05). Serum YKL-40 level was negatively correlated with serum IgG level (r=-0.309, P=0.047) and serum complement 4 level (r=-0.324, P=0.039). The area under the ROC curve of serum YKL-40 level for diagnosing recurrent pneumonia was 0.958 (95%CI: 0.921-0.994).

CONCLUSIONSHumoral immune function is low in children with recurrent pneumonia. Serum YKL-40 may be involved in the occurrence of recurrent pneumonia and can be used as a reference index for diagnosing recurrent pneumonia.