Abstract: Objective To investigate the expression and clinical significance of blood lactic acid, Clara cell secretory protein (CCSP) and interleukin-22 receptor (IL-22R) in children with pneumonia. 
Methods A total of 150 children with pneumonia treated in our hospital were selected as the observation group. They were divided into 96 cases in the acute phase and 54 cases in the convalescent phase according to the course of disease, and were divided into mild disease group and severe disease group according to the severity of the disease. Another 80 healthy children during the same period were selected as the control group. The levels of blood lactic acid, CCSP, and IL-22R in the control group, acute phase and convalescent phase were compared, and these levels in children with different conditions in the acute phase and convalescent phase were compared. The correlation between the levels of blood lactic acid, CCSP and IL-22R in children with pneumonia and the value of blood lactic acid, CCSP and IL-22R alone and in combination in the diagnosis of pneumonia were analyzed, and the receiver operating characteristic (ROC) curve was drawn. 
Results Blood lactic acid and IL-22R in the control group were lower than those in the acute and convalescent phase groups, and lower in the convalescent group than in the acute group (P＜0.05). CCSP in the control group was higher than that in the acute and convalescent groups, and higher in the convalescent group than in the acute group (P＜0.05). In the acute phase group, the levels of blood lactic acid and IL-22R in severe group A were higher than those in mild group A, while CCSP was lower than that in mild group A (P＜0.05). In the convalescent group, the levels of blood lactic acid and IL-22R in severe group B were higher than those in mild group B, while CCSP was lower than that in mild group B (P＜0.05). Pearson correlation analysis showed that blood lactic acid and IL-22R were negatively correlated with CCSP in children with acute pneumonia (r=-0.75, 0.81, P＜0.05), and blood lactic acid was positively correlated with IL-22R (r=0.06, P＜0.05). There was no correlation between blood lactic acid, CCSP and IL-22R in children in convalescent phase (P＞0.05). The area under the ROC curve (AUC) of blood lactic acid, CCSP and IL-22R in combination in the diagnosis of pediatric pneumonia was higher than that of single detection (P＜0.05). 
Conclusion The expression of blood lactic acid and IL-22R is high, while the expression of CCSP is low in children with pneumonia. The abnormal levels can indicate severe pneumonia. The combined detection of blood lactic acid, CCSP and IL-22R has high value in the diagnosis of children with pneumonia.

Key words: pneumonia, lactic acid, Clara cell secretory protein, IL-22 receptor