**Question:** Investigation of choice for bronchiectasis is: September 2009

**Core Concept:** Bronchiectasis is a condition characterized by irreversible dilation of the bronchi, leading to chronic respiratory infections and potential severe respiratory compromise. The appropriate investigations help in diagnosis, assessing severity, and monitoring treatment response.

**Why the Correct Answer is Right:** The correct answer is computed tomography (CT) scan. A CT scan is the most sensitive and specific imaging modality for detecting bronchiectasis. It clearly shows the extent, location, and severity of bronchial wall thickening and airway dilation. Bronchiectasis can be classified as central, peripheral, or mixed. In addition, CT imaging aids in differentiating bronchiectasis from other conditions like asthma or cystic fibrosis, which may present with similar symptoms and signs.

**Why Each Wrong Option is Incorrect:**

A. Chest X-ray (CXR): While CXR can show bronchiectasis, it lacks the resolution to demonstrate the specific features of bronchiectasis. Additionally, the extent of disease, its classification, and differentiation from other conditions are better demonstrated with CT scan.

B. Pulmonary function tests (PFTs): PFTs assess lung function but do not directly visualize the bronchiectasis itself. They provide information about lung volumes, flows, and diffusion capacity, which may be abnormal in bronchiectasis but do not serve as the primary investigation for bronchiectasis.

C. Spirometry: Similar to PFTs, spirometry is a tool for assessing lung function but does not directly visualize the condition. Spirometry may reveal airflow obstruction, reduced lung volumes, or impaired diffusion capacity, which could be seen in bronchiectasis, but it is not the primary investigation for bronchiectasis.

D. Blood tests: Blood tests, including complete blood count (CBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), assess systemic inflammation and infection but do not specifically diagnose bronchiectasis. Bronchiectasis is a disease of the respiratory system, and these tests assess the general body response to inflammation and infection, not bronchiectasis itself.

**Core Concept:** The correct answer is CT scan, as it provides detailed imaging of bronchiectasis, classifies the disease, and differentiates it from other respiratory conditions like asthma or cystic fibrosis.

**Why Each Wrong Option is Incorrect:**

A. Chest X-ray (CXR): CXR is less sensitive and specific than CT scan for detecting bronchiectasis, particularly in its early stages or in the absence of significant consolidation or pleural effusion.

B. Pulmonary function tests (PFTs): As mentioned earlier, PFTs assess lung function, which may be abnormal in bronchiectasis, but these tests are not the primary investigation for bronchiectasis.

C. Spirometry: Similar to PFTs, spirometry assesses lung function and cannot directly visualize bronchiectasis. The results may be abnormal in bronchiectasis but are not the primary investigation for