A 6-year-old child from rural India presents with persistent cough for 3 weeks, low-grade fever, and weight loss. Chest X-ray shows a right hilar opacity with mediastinal lymphadenopathy. Tuberculin skin test (TST) is positive (15 mm induration). What is the most appropriate next investigation to confirm pulmonary tuberculosis?

## Investigation of Choice for Pediatric Pulmonary TB ### Why Gastric Lavage is the Gold Standard in Children **Key Point:** Children with pulmonary TB typically cannot produce sputum spontaneously due to weak cough mechanics and swallowing of respiratory secretions. Gastric lavage (aspiration of gastric contents in the early morning) recovers swallowed sputum and allows AFB smear microscopy and culture. ### Diagnostic Approach in Pediatric TB | Investigation | Sensitivity | Specificity | When Used | Limitations | |---|---|---|---|---| | **Gastric lavage (AFB + culture)** | 40–60% | High | **First-line in children <10 years** | Requires early morning sampling; multiple attempts may be needed | | Sputum smear microscopy | 80–90% | High | Adolescents & adults; older children who can expectorate | Most children cannot produce sputum | | Bronchoscopic BAL | 70–80% | High | When gastric lavage fails; immunocompromised children | Invasive; requires expertise; reserved for difficult cases | | HRCT chest | High | Moderate | Adjunctive; assesses extent & complications | Cannot confirm TB; radiation exposure | ### Clinical Pearl **High-Yield:** In children <10 years with suspected pulmonary TB, gastric lavage is the investigation of choice for microbiological confirmation. The procedure is performed on an empty stomach (early morning), and the aspirate is sent for: - AFB smear microscopy (Ziehl-Neelsen or auramine-rhodamine staining) - Culture on Löwenstein-Jensen medium (gold standard for confirmation) - Gene Xpert MTB/RIF (rapid, WHO-recommended; detects TB and rifampicin resistance in ~2 hours) ### Why Other Options Are Less Appropriate **Sputum smear microscopy** — Children rarely expectorate sputum; this is the investigation of choice in adolescents and adults who can produce adequate samples. **HRCT chest** — Provides anatomical detail but cannot microbiologically confirm TB; used to assess extent of disease and complications (cavitation, bronchiectasis) after diagnosis is established. **Bronchoscopic BAL** — Invasive and reserved for cases where gastric lavage has failed or in immunocompromised children; not first-line. [cite:Park 26e Ch 8]