## Investigation of Choice for TB Case Detection at SC Level ### Role of Sub-Centre in TB Diagnosis **Key Point:** The Sub-Centre is the first point of contact in the Indian public health system and must be equipped to perform the most practical, cost-effective, and sensitive screening investigation for TB. **High-Yield:** Sputum smear microscopy (Ziehl-Neelsen staining) is the investigation of choice at the Sub-Centre level because: 1. **Feasibility** — Requires minimal infrastructure; can be done at the SC 2. **Cost-effectiveness** — Inexpensive and sustainable in resource-limited settings 3. **Sensitivity for infectious TB** — Detects smear-positive (infectious) cases, which is the public health priority 4. **NTEP guideline** — National TB Elimination Programme (NTEP) mandates sputum microscopy as the first-line investigation at peripheral health facilities 5. **Turnaround time** — Results available within 24–48 hours ### Why Sputum Smear Microscopy? | Feature | Sputum Smear | Chest X-ray | GeneXpert MTB/RIF | TST | |---------|--------------|-------------|-------------------|-----| | **Available at SC** | Yes | No | No (reserved for CHC/PHC) | Yes, but not diagnostic | | **Cost** | Very low | High | High | Low | | **Identifies infectious cases** | Yes (smear+) | No | Yes | No | | **Diagnostic test** | Yes | Supportive | Yes | Screening only | | **NTEP recommendation** | First-line | Confirmatory | Confirmatory (if available) | Screening | **Clinical Pearl:** A smear-positive case is immediately infectious and a public health priority. The SC worker must identify these cases and refer for treatment initiation at the PHC/CHC. **Mnemonic:** **SPUTUM** = **S**creening, **P**eripheral, **U**seful, **T**imely, **U**niversal, **M**icroscopy
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