<b>DIAGNOSTIC ACCURACY OF LUNG ULTRASOUND IN DIAGNOSING PNEUMOTHORAX TAKING HRCT AS GOLD STANDARD</b>

Background: Pneumothorax needs to be diagnosed promptly and correctly and lung ultrasound has become a quicker bedside alternative to traditional imaging. The aim of this research is to establish the diagnostic efficiency of lung ultrasound in diagnosing pneumothorax with HRCT chest serving as the gold standard. Research design: Cross-sectional validation research. Place and duration of study: Department of Radiology, Combined Military Hospital, Gujranwala, from 30th December 2023 and 1st December 2024. Material and Methods: 205 patients with a clinical suspicion of pneumothorax were recruited using non-probability consecutive sampling. Both male and female adult patients were considered and those who were hemodynamically unstable, required urgent intervention, had previously received chest tube placement, widespread subcutaneous emphysema, or had incomplete imaging data were excluded. Lung ultrasound and HRCT chest were performed on all patients within the same clinical episode. Diagnostic indices, such as sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and likelihood ratios, were calculated. The stratification was also conducted on the basis of the key demographic and clinical variables. Results: The mean age of the patients was 45.56 ± 14.65 years, mean BMI was 25.89 ± 5.30 kg/m², and mean duration of symptoms was 48.62 ± 41.55 hours. Study population was male dominant. The pneumothorax was detected in 26 patients (12.7% by HRCT and 40 patients (19.5% by lung ultrasound). Cross-tabulation revealed that there were 21 true positives, 160 true negatives, 19 false positives, and 5 false negatives. The sensitivity of lung ultrasound was 80.8, specificity was 89.4, positive predictive value was 52.5, negative predictive value was 97.0, and the overall diagnostic accuracy was 88.3. Its positive likelihood ratio was 7.61 and the negative likelihood ratio was 0.22. When stratified, specificity was consistently high in most subgroups but sensitivity varied according to age, BMI, length of symptoms and etiology. Conclusion: Lung ultrasound demonstrated excellent diagnostic efficacy in the diagnosis of pneumothorax in comparison with HRCT chest. Its high negative predictive value and good likelihood ratios corroborate its use as a fast bedside screening instrument especially as a means of eliminating pneumothorax in acute clinical cases. Nevertheless, since false-positive and false-negative results occur in certain subgroups, HRCT is still significant to confirm in the case of equivocality or high-risk.