BACKGROUND: Primary spontaneous pneumothorax (PSP) is a common condition encountered in emergency departments, typically affecting young, otherwise healthy individuals. Identifying patients at risk for recurrence is critical for optimizing management strategies and preventing complications. This study aimed to evaluate the predictive value of the Haller index in determining the risk of recurrence in patients diagnosed with PSP. METHODS: A retrospective analysis was conducted on patients diagnosed with PSP between January 1, 2019 and January 1, 2024, in the emergency department of a tertiary care hospital. Patients were categorized into two groups: those experiencing a single PSP episode and those with recurrent pneumothorax. Propensity score matching was employed to control for confounders, including age, gender, smoking status, and body mass index (BMI). The Haller index was calculated from chest computed tomography (CT) scans, and its predictive accuracy for recurrence was evaluated using Receiver Operating Characteristic (ROC) curve analysis. RESULTS: A total of 182 patients were included in the study, with 91 patients in each group after propensity score matching. The Haller index was significantly higher in the recurrent pneumothorax group (2.72+-0.47) compared to the single pneumothorax group (2.15+-0.34), with a mean difference of 0.56 (95% confidence interval [CI]: 0.44-0.69, p<
0.001). ROC analysis demonstrated an area under the curve (AUC) of 0.830 (95% CI: 0.768-0.882), with a Youden index of 0.50, sensitivity of 72.53%, and specificity of 76.92% for a cutoff value of >
2.38. CONCLUSION: The Haller index is a strong predictor of recurrent pneumothorax in patients with PSP. Its integration into clinical assessments can help identify patients at elevated risk of recurrence, enabling tailored treatment strategies.