**Core Concept:**
The question is about the fastest method for diagnosing tuberculosis (TB), which is a bacterial infection caused by Mycobacterium tuberculosis. Diagnosis of TB is crucial to initiate appropriate treatment and prevent further spread of the disease.

**Why the Correct Answer is Right:**
The correct answer, **D.** **Bronchoscopy with bronchoalveolar lavage (BAL)**, is the fastest method for diagnosing TB due to its ability to directly obtain Mycobacterium tuberculosis from the respiratory tract. BAL involves inserting a flexible tube (bronchoscope) into the airways and collecting fluid or cells for laboratory examination. This method provides a higher sensitivity and specificity compared to other diagnostic methods, such as sputum examination or blood tests.

**Why Each Wrong Option is Incorrect:**
A. **Sputum examination:** While sputum examination is a common method for TB diagnosis, it has a lower sensitivity due to the difficulty of patients to produce quality sputum samples.
B. **Blood tests (e.g., interferongamma release assays, culture of blood samples):** Blood tests have limited sensitivity in detecting TB and may not be specific enough to differentiate TB from other mycobacterial infections or latent TB infections.
C. **Imaging studies (X-ray, CT scan):** Although imaging studies help identify the presence of TB lesions, they do not directly provide a diagnosis of TB and are not as sensitive as BAL or sputum examination.

**Clinical Pearl / High-Yield Fact:**
Diagnosing TB requires a combination of clinical, radiological, and laboratory investigations. However, for an accurate and rapid diagnosis, **BAL** is the preferred method due to its high sensitivity and specificity.

By using a combination of these diagnostic methods, healthcare professionals can confidently diagnose TB, initiate appropriate treatment, and prevent the spread of the disease.