Okay, let's tackle this question. The question is asking which screening method is used under RNTCP, which stands for the Revised National Tuberculosis Control Programme in India. The user hasn't provided the options, but I need to figure out the correct answer based on common knowledge.

First, the core concept here is understanding the screening methods employed by RNTCP. RNTCP primarily focuses on tuberculosis control. The standard method for TB detection has been sputum smear microscopy, especially the Ziehl-Neelsen stain. This method is cost-effective and widely used in resource-limited settings. More advanced methods like GeneXpert might be used now, but RNTCP traditionally relied on sputum smear.

The correct answer is likely AFB (Acid-Fast Bacilli) smear microscopy. Let me confirm: RNTCP uses sputum smear microscopy as the primary screening tool. Other methods like chest X-ray or culture might be part of the process but aren't the primary screening method. So the correct answer is AFB smear.

Now, the distractors. If the options include chest X-ray, culture, or nucleic acid amplification tests (like GeneXpert), those would be incorrect. Chest X-ray is used for initial assessment but not for screening. Culture is more accurate but takes longer. GeneXpert is rapid but more expensive and not the primary method in RNTCP.

Clinical pearl: Remember that RNTCP emphasizes sputum smear microscopy for TB screening. The AFB smear is the cornerstone. Also, DOTS strategy is the treatment approach, but screening is done via smear.

Putting it all together, the correct answer is AFB smear microscopy. Let me structure the explanation with the required sections, making sure each part is concise and fits within the character limit.

**Core Concept**
The Revised National Tuberculosis Control Programme (RNTCP) in India employs **sputum smear microscopy** as the primary screening method for tuberculosis. This method detects *Mycobacterium tuberculosis* using **Ziehl-Neelsen staining** of sputum samples, which is cost-effective and suitable for resource-limited settings.

**Why the Correct Answer is Right**
**Acid-fast bacilli (AFB) smear microscopy** is the cornerstone of RNTCP for initial TB screening. It identifies acid-fast bacilli in sputum by staining with carbol-fuchsin and counterstaining with methylene blue. While not the most sensitive method, it is rapid, affordable, and widely implemented in public health systems like RNTCP to triage patients for further diagnostic workup.

**Why Each Wrong Option is Incorrect**
**Option A:** *Chest X-ray* is used for **diagnostic evaluation** or **active case finding** in high-risk populations but not as the **primary screening tool** in RNTCP.
**Option B:** *Nucleic acid amplification tests (NAATs)* like GeneXpert are **not standard** in RNTCP due to cost and infrastructure constraints, though they may be used in advanced settings.
**Option C:** *Culturing* is **not used for initial screening** because it requires specialized labs and 2–6 weeks for results, delaying treatment initiation.

**Clinical Pearl / High-Yield Fact**
Never confuse **screening methods** with **diagnostic methods** in TB programs

✓ Correct Answer: B. Passive