Opportunistic osteoporosis screening in fibrosing interstitial lung disease using chest CT-derived vertebral Hounsfield units

Osteoporosis is a common but often under-recognized comorbidity in fibrosing interstitial lung diseases (FILD), partly because dual-energy X-ray absorptiometry (DXA) is not routinely integrated into respiratory care. Chest computed tomography (CT), performed regularly for FILD monitoring, typically includes T12–L2 and may allow opportunistic vertebral Hounsfield unit (HU) assessment. Whether CT-derived HU can identify osteoporosis in FILD remains unclear. In this retrospective study, 111 patients with FILD who had both chest CT and DXA performed within a 90-day interval were included in the analysis. HU values at T12, L1, and L2 and their mean were measured. Osteoporosis was defined based on the lowest T-score among the lumbar spine, total hip, or femoral neck. Correlation analyses, multivariable logistic regression, and ROC analyses were performed. Thirty-six patients (32.4%) had osteoporosis. HU values at all levels were significantly lower in osteoporotic patients (p < 0.001) and correlated with DXA T-scores (r = 0.496–0.644). HU remained an independent predictor of osteoporosis after adjustment for age, BMI, sex, and glucocorticoid use. ROC curves showed good discrimination, with AUCs of 0.789 (T12), 0.823 (L1), 0.806 (L2), and 0.818 (mean T12–L2). The mean HU provided the highest Youden index and the best balance of sensitivity (83.3%) and specificity (72.0%). Chest CT-derived vertebral HU can be used as an opportunistic screening marker for osteoporosis in FILD, with mean HU providing a practical parameter to prompt further DXA evaluation.