Purpose: To measure serum PTX3 levels in patients admitted with right lower quadrant pain to emergency department and to investigate whether this parameter will be helpful for the diagnosis of acute appendicitis. Materials and methods: This study was conducted with a group of 89 patients over 17 years of age who were admitted with the complaint of right lower quadrant pain to ED and had a preliminary diagnosis of acute appendicitis clinically and the control group of 31 healthy volunteers in a tertiary university hospital for 3 months. Results: Median PTX3 levels were 3.28 (1.08-30.24) ng/mL in the acute appendicitis groups and 0.97 (0.34-2.62) ng/mL in the control group. A significant difference was observed between acute appendicitis groups and the control group (p < 0.05). Conclusion: PTX3 was found to be significantly higher in patient with acute appendicitis compared to the control group and the patients with non-specific abdominal pain. PTX3 can be used as an aid in the diagnosis of acute appendicitis.