## **Core Concept**
The patient presents with symptoms of hemoptysis, which is the coughing up of blood or blood-stained mucus from the respiratory tract. This symptom can be indicative of various serious conditions, especially in a chronic smoker, suggesting a possible malignancy or chronic obstructive pulmonary disease (COPD). Given that the chest X-ray appears normal, further investigation is required to identify the source of bleeding.

## **Why the Correct Answer is Right**
The correct answer, **High-Resolution Computed Tomography (HRCT)**, is the next best investigation in this scenario. HRCT is more sensitive than a standard chest X-ray and can detect abnormalities in the lung parenchyma, airways, and peripheral structures. It is particularly useful for identifying conditions such as bronchiectasis, small peripheral lung cancers, and other focal lung lesions that might not be visible on a standard chest X-ray. In a chronic smoker with hemoptysis and a normal chest X-ray, HRCT can help in early detection and characterization of the underlying pathology.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While a standard chest X-ray has already been performed and appears normal, repeating it may not yield additional information.
- **Option B:** A Mantoux test (tuberculin skin test) is used to assess if a person has been infected with Mycobacterium tuberculosis. Although tuberculosis can cause hemoptysis, the patient's presentation and a normal chest X-ray do not specifically suggest TB as the first consideration.
- **Option C:** Bronchoscopy is an important diagnostic tool for hemoptysis, especially when the cause is not identified by imaging or when there is significant bleeding. However, it is usually considered after imaging studies like HRCT, given its invasive nature.
- **Option D:** While pulmonary function tests (PFTs) can be useful in assessing lung function, especially in conditions like COPD, they are not the immediate next step in investigating the cause of hemoptysis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in the management of hemoptysis is that even if the chest X-ray is normal, further evaluation with HRCT and possibly bronchoscopy is often required, especially in high-risk patients like smokers, to rule out serious conditions such as lung cancer or pulmonary embolism.

## **Correct Answer:** . **High-Resolution Computed Tomography (HRCT)**