What procedure provides a definitive diagnosis of tuberculosis in a 20-year-old with a positive TB skin test?

A sputum specimen is the procedure that provides a definitive diagnosis of tuberculosis (TB). When a patient has a positive TB skin test, it indicates that they have been exposed to the TB bacteria, but further testing is necessary to confirm the presence of active TB disease.

Collecting a sputum specimen allows for the direct identification of Mycobacterium tuberculosis through microscopic examination, culture, or molecular testing. This is crucial because a positive skin test alone does not confirm the disease; it may indicate latent TB. By analyzing the sputum, healthcare providers can assess whether the bacteria are actively replicating and if the patient is infectious.

While bronchoscopy can also be used to obtain samples from deeper within the lungs, it is generally reserved for cases where sputum samples are inconclusive or when there are specific complications. A chest X-ray is helpful in identifying signs of TB in the lungs, but it does not provide definitive evidence of the active disease or identify the bacterium itself. A complete blood count, while useful for assessing overall health, does not specifically relate to diagnosing tuberculosis.