CD4 T-Lymphocyte Depletion as an Indicator of Cavitary Tuberculosis in HIV Co-infection

Background. Cavitary tuberculosis is the most destructive manifestation of pulmonary TB in HIV co-infection, driving community transmission through high bacillary loads. Despite established links between preserved CD4 function and granulomatous cavitation, clinicians in high-burden settings lack a quantitative immune threshold for risk stratification. In Nigeria, where the HIV-TB syndemic remains severe, such a threshold could inform triage and infection control decisions. Objectives. To derive a validated CD4 count threshold for identifying cavitary pulmonary TB in HIV-positive adults at a Nigerian tertiary hospital. Methods. Case-control study at Delta State University Teaching Hospital, Nigeria (2017-2020). Cases: HIV-positive adults with bacteriologically confirmed cavitary pulmonary TB (n=13). Controls: HIV-positive adults with non-cavitary pulmonary TB (n=94), matched by age and sex. CD4 was measured by flow cytometry within a median of 7 days (IQR 3-14 days) of chest radiography; 89% of measurements were performed within 14 days. Two radiologists, blinded to CD4 and HIV status, independently scored chest radiographs using the Chest Radiograph Reading and Recording System. Association was quantified by Firth penalised exact logistic regression; discriminative accuracy by ROC analysis. Sensitivity analysis restricted to CD4 measured within 14 days of imaging (n=95) confirmed robustness. Results. CD4 >=200 cells/mL was associated with cavitary TB (OR 17.2, 95% CI 4.1-89.6). ROC AUC was 0.84 (95% CI 0.72-0.96). Sensitivity 61.5%, specificity 91.5%, PPV 50.0%, NPV 94.5%. Zero cavitation occurred below CD4 100 (0/48). The graded relationship showed 0% cavitation at CD4 <100, 11.6% at 100-199, 46.2% at 200-349, and 66.7% at >=350 cells/mL (chi-square for trend p < 0.001). In sensitivity analysis (CD4 within 14 days of imaging), the association remained materially unchanged (OR 16.8, 95% CI 3.9-88.1). Conclusions. CD4 counts at or above 200 cells/mL identify HIV-positive patients at risk of cavitary pulmonary TB. This readily available threshold may guide risk stratification and infection control in high-burden TB-HIV programmes. Prospective multicentre validation is warranted. Trial registration: Not applicable. Observational study. Funding: This research received no external funding.