A Multidisciplinary-Validated Radiographic Severity Score for Immune Stratification in HIV-Associated Tuberculosis: Development and Internal Validation

Background: Human immunodeficiency virus (HIV)-associated tuberculosis (TB) remains the leading cause of death among people living with HIV in sub-Saharan Africa. Where CD4 testing is unavailable, a chest X-ray must substitute for flow cytometry. We developed and internally validated a Radiographic Severity Score (RSS) to identify HIV-positive patients with advanced immunosuppression using plain-film radiography. Methods: Cross-sectional diagnostic accuracy study of 242 HIV-positive adults with newly diagnosed pulmonary TB at two sites in southern Nigeria (2017-2018). Two radiologists independently scored films using the RSS (12 zones, weighted for severity). Discriminative accuracy, calibration, and inter-reader reliability were assessed. Results: Of 242 enrolled, 228 had complete data. Mean RSS was 2.2±1.5 (CD4 <100 cells/µL), 3.4±1.7 (CD4 100-199 cells/µL), 4.8±1.9 (CD4 200-349 cells/µL), and 6.1±1.8 (CD4≥350 cells/µL). The stepwise gradient was significant (Spearman rho =+0.72, p <0.001). At threshold RSS ≤4: AUC=0.84 (95% CI 0.76-0.92), sensitivity 68.3%, specificity 80.0%, PPV 79.5%, NPV 69.4%. Inter-reader agreement was almost perfect (Cohen kappa =0.81, ICC=0.92). Conclusion: The RSS is a simple bedside tool for identifying HIV-positive patients with CD4 <200 cells/µL in settings without same-day CD4 testing. In this Nigerian cohort, the RSS demonstrated strong discriminative accuracy (AUC 0.84) and almost perfect inter-reader reliability (kappa 0.81). However, external validation in independent cohorts is required before the RSS can be recommended for widespread implementation in TB-HIV integrated programmes.