A 35-year-old woman from a rural village in Madhya Pradesh attends the Primary Health Centre (PHC) with complaints of persistent cough for 3 weeks and low-grade fever. The health worker suspects tuberculosis. Which is the investigation of choice for initial screening and diagnosis at the PHC level?

Explanation

## Investigation of Choice for TB Screening at PHC Level **Key Point:** Sputum smear microscopy (Ziehl-Neelsen staining) remains the gold standard first-line investigation for TB diagnosis at the Primary Health Centre level in India, as per NTEP (National TB Elimination Programme) guidelines. ### Why Sputum Smear Microscopy? 1. **Feasibility at PHC**: Requires minimal infrastructure, low cost, and can be performed at peripheral health facilities. 2. **High Specificity**: Direct visualization of acid-fast bacilli is highly specific for TB diagnosis. 3. **Infectious TB Detection**: Identifies smear-positive cases, which are the most infectious and epidemiologically important. 4. **NTEP Protocol**: Recommended as the first investigation for presumptive TB cases in the national programme. ### Investigation Algorithm for TB at PHC ```mermaid flowchart TD A[Presumptive TB Case]:::outcome --> B[Sputum Smear Microscopy x2]:::action B --> C{Smear Positive?}:::decision C -->|Yes| D[Confirm TB, Start DOTS]:::action C -->|No| E[Clinical Assessment + CXR]:::action E --> F{Suggestive of TB?}:::decision F -->|Yes| G[Refer for GeneXpert MTB/RIF]:::action F -->|No| H[Investigate for other causes]:::action ``` **High-Yield:** At PHC level, sputum smear microscopy is the primary investigation. GeneXpert MTB/RIF (CBNAAT) is reserved for: - Smear-negative symptomatic cases - TB-HIV co-infection - Drug-resistant TB suspects - Pediatric TB (where sputum collection is difficult) **Clinical Pearl:** The PHC worker must collect early morning sputum (first expectoration of the day) for maximum bacillary load. Two consecutive sputum samples are examined — if either is positive, TB is confirmed. **Mnemonic:** **SSM-PHC** = Sputum Smear Microscopy at Primary Health Centre is the first-line investigation. [cite:Park 26e Ch 6]