## Clinical Context This patient has: - Severe immunosuppression (CD4 < 200 cells/μL) - Atypical TB presentation (bilateral perihilar infiltrates, minimal upper lobe disease) - Negative sputum smears on two occasions (smear-negative TB) In advanced HIV, TB often presents with atypical radiological patterns and lower bacterial burden, making sputum smear microscopy unreliable. ## Why Sputum Induction or BAL? **Key Point:** Smear-negative TB in immunocompromised patients requires enhanced diagnostic methods to isolate *Mycobacterium tuberculosis* and confirm diagnosis before therapy. **High-Yield:** Sputum induction (using hypertonic saline nebulization) or BAL: - Increases diagnostic yield in smear-negative cases from ~30% to 60–80% - Allows mycobacterial culture (gold standard) - Permits drug sensitivity testing (critical in HIV with high MDR-TB risk) - Identifies alternative diagnoses (PCP, MAC, CMV, fungal infections) **Clinical Pearl:** In CD4 < 200, TB often presents with: - Atypical CXR patterns (mediastinal lymphadenopathy, minimal cavitation) - Lower sputum bacillary load (smear-negative) - Extrapulmonary TB (lymph nodes, disseminated) ## Diagnostic Algorithm for Smear-Negative TB in HIV ```mermaid flowchart TD A[Smear-negative, CD4 < 200, TB suspected]:::outcome --> B{Sputum quality adequate?}:::decision B -->|Yes, repeat smear| C[Sputum induction or BAL]:::action B -->|No| C C --> D[AFB smear + culture + DST]:::action D --> E{TB confirmed?}:::decision E -->|Yes| F[Start anti-TB therapy]:::action E -->|No| G[Investigate alternative diagnosis]:::action ``` **Mnemonic:** **SPUTUM** in smear-negative TB = **S**putum induction, **P**rocedure (BAL), **U**ndergo culture, **T**est for DST, **U**nderstand CD4 status, **M**ultiple samples if needed. 
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