Abstract: Objective To investigate the changes of serum matrix metalloproteinase-9 (MMP-9), serum amyloid A (SAA) and trypsinogen-2 (TPS-2) levels in patients with acute pancreatitis (AP) of different severity. 
Methods A retrospective analysis was conducted on the clinical data of 84 patients with AP admitted to Liaocheng People′s Hospital in Shandong Province. Based on their Acute Physiology and Chronic Health Evaluation Ⅱ (APACHE Ⅱ) scores, the patients were divided into the severe group (APACHE Ⅱ score ≥ 8 points, n=30) and the mild group (APACHE Ⅱ score＜8 points, n=54). Additionally, 50 healthy physical examinees were selected as controls. The differences in MMP-9, SAA, and TPS-2 between the patient group and the control group were compared, and the general information and serum MMP-9, SAA, and TPS-2 levels of patients with different severity were observed. The risk factors for the progression of AP to severe AP were identified through multiple Logistic regression analysis. Receiver operating characteristic (ROC)curve was used to analyze the value of serum MMP-9, SAA, and TPS-2 in predicting severe AP. 
Results Serum levels of MMP-9, SAA and TPS-2 in patient group were significantly higher than those in control group (P＜0.05). The serum levels of MMP-9, SAA and TPS-2 in the severe group were (610.48±178.25) μg/L, (597.67±168.49) mg/L and (244.56±80.11) kU/L, respectively, which were significantly higher than those in the mild group ［(346.77±113.23) μg/L, (339.78±107.66) mg/L, (64.76±21.07) kU/L］ (P＜0.05). Multivariate Logistic regression analysis showed that high levels of serum MMP-9 (OR=2.688, 95%CI: 1.351-5.348), SAA (OR=3.273, 95%CI: 1.509-7.099), and TPS-2 (OR=2.817, 95%CI: 1.418-5.596) were the risk factors for the progression ofAP to severe AP in patients (P＜0.05). ROC analysis showed that the area under the ROC curve (AUC) of serum MMP-9, SAA and TPS-2 in predicting severe AP was 0.831, 0.888 and 0.841, respectively, the sensitivity was 0.767, 0.800 and 0.733, respectively, and the specificity was 0.833, 0.926 and 0.870, respectively (all with P＜0.05). 
Conclusion Serum MMP-9, SAA, and TPS-2 levels can predict the severity of AP to a certain extent, and can be used as serum indexes to predict severe AP. 

Key words: pancreatitis, matrix metalloproteinase-9, amyloid A, trypsinogen 2