## **Core Concept**
The Revised National Tuberculosis Control Programme (RNTCP) in India focuses on the control and prevention of tuberculosis (TB) through systematic screening and treatment. The program emphasizes the identification of sputum smear-positive cases as the primary source of infection. Screening under RNTCP is crucial for early detection and treatment of TB.

## **Why the Correct Answer is Right**
The correct answer, **D. Sputum smear microscopy**, is right because RNTCP emphasizes sputum smear microscopy as the primary method for screening and diagnosing pulmonary tuberculosis. This method is rapid, cost-effective, and can be implemented in resource-limited settings. It targets the detection of acid-fast bacilli (AFB) in sputum, which are indicative of active TB infection.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Chest X-ray is a useful diagnostic tool but is not the primary method emphasized by RNTCP for screening due to its higher cost and the need for specialized equipment and expertise.
- **Option B:** Mantoux test (tuberculin skin test) is used to detect latent TB infection but is not the primary screening tool under RNTCP for active disease.
- **Option C:** Culture for Mycobacterium tuberculosis is the gold standard for diagnosing TB but is not used for initial screening under RNTCP due to its longer turnaround time and higher cost.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that RNTCP's strategy focuses on **sputum smear-positive pulmonary TB** as the main source of transmission. Therefore, sputum smear microscopy is the cornerstone of TB screening under this program. This approach allows for early initiation of treatment and reduction of transmission in the community.

## **Correct Answer:** D. Sputum smear microscopy