Diagnostic Accuracy of Lung Ultrasound vs Chest Radiography for Detection of Interstitial Syndrome: A Computed Tomography-referenced Comparative Study

Background and aim: Interstitial syndrome represents an important radiological finding in patients with various pulmonary pathologies.While computed tomography (CT) remains the reference standard for diagnosis, the utility of lung ultrasound (LUS) compared with chest radiography (CXR) as an initial diagnostic modality remains incompletely defined.This study aimed to compare the diagnostic accuracy of LUS and CXR for detecting interstitial syndrome using CT as the reference standard.Materials and methods: This retrospective observational study was conducted at a tertiary care center from October 2024 to June 2025.We analyzed 167 consecutive adult patients who underwent LUS, CXR, and CT within 24 hours for the evaluation of suspected interstitial syndrome or interstitial lung disease (ILD).Standard diagnostic performance metrics-sensitivity, specificity, positive and negative predictive values (PPV and NPV), the diagnostic odds ratio (DOR), likelihood ratios (LR+ and LR-), and overall accuracy-were calculated for both modalities using CT as the reference.Diagnostic concordance of these modalities with CT was addressed using Cohen's kappa, and systematic diagnostic disagreement was evaluated by McNemar's test.Ninety-five percent CIs were calculated.Results: Computed tomography identified interstitial syndrome in 64 of 167 patients (38.3%).Lung ultrasound demonstrated sensitivity of 92.2% (95% CI 82.7-97.4%),specificity of 94.2% (95% CI 87.8-97.8%), a PPV of 90.8%, an NPV of 95.1%, a DOR of 190.8, and overall accuracy of 93.4%.Chest radiography showed sensitivity of 67.2% (95% CI 54.3-78.4%), a specificity of 91.3% (95% CI 84.1-95.9%), a PPV of 82.7%, an NPV of 81.7%, a DOR of 21.4, and an accuracy of 82.0%.Agreement was substantially higher for LUS (κ = 0.861) than for CXR (κ = 0.606).McNemar's test confirmed a systematic diagnostic disagreement between the two modalities (p = 0.012).Conclusion: Lung ultrasound demonstrated superior diagnostic accuracy compared with CXR for detecting interstitial syndrome.These findings suggest that LUS may be a clinically useful first-line assessment tool, particularly in settings where trained operators are available.Computed tomography remains indispensable for etiologic characterization. Clinical significance:In resource-constrained healthcare settings where CT availability is limited-a scenario common to many centers across India-LUS performed by trained pulmonologists may offer a pragmatic, radiation-free alternative for identifying interstitial syndrome at the point of care.The high NPV of LUS is particularly relevant for safely excluding significant interstitial disease in the appropriate clinical context.