Objective: To investigate the value of pleural effusion combined with determination of serum monocyte chemotactic protein 1 (MCP-1) and soluble triggering receptor on myeloid cells 1 (sTREM-1) in early predicting the severity of acute pancreatitis (AP). 
Methods: The clinical data of 75 AP patients treated from December 2017 to December 2018 were collected. According to the severities of disease, the patients were divided into mild AP group (31 cases) and non-mild AP group (44 cases). The presence of pleural effusion at admission and other clinical variables were compared between the two groups, and the differences of serum levels of MCP-1 and sTREM-1 in the two groups of patients from the healthy subjects as well as their dynamic changes were also analyzed.
Results: There were no significant difference in sex, age and pathogenesis between the two groups, but the C-reaction protein (CRP) level, APACHE II score and incidence of pleural effusion were significantly higher and length of hospital stay was significantly longer in non-mild AP group than those in mild AP group (all P<0.05). The serum levels of MCP-1 and sTREM-1 in either mild AP group or non-mild AP group were significantly higher than those in healthy control group, but both in non-mild AP group were continuously and significantly higher than those in mild AP group (all P<0.05). Results of analysis of the predictive abilities for severity of AP by using CRP (≥98.55 mg/L), APACHE II score (≥8), pleural effusion and serum levels of MCP-1 (≥27.84 pg/mL) and sTREM-1 (≥0.39 ng/mL) alone or combinations showed that pleural effusion combined with serum MCP-1 and sTREM-1 had the highest estimation value (AUC=0.884, with a sensitivity of 93.2% and a specificity of 91.3%). 
Conclusion: Pleural effusion combined with serum MCP-1 and sTREM-1 detection has certain value for early predicting the severity of AP.