A lab technician with a positive Mantoux test shows 10.5 mm redness. What is the next best step?

A positive Mantoux test, which measures delayed-type hypersensitivity to the tuberculin purified protein derivative, indicates possible exposure to Mycobacterium tuberculosis. The size of the induration, which in this case is 10.5 mm, suggests a significant reaction, especially in a lab technician who may have higher risk factors for tuberculosis due to occupational exposure.

The next best step following a positive Mantoux test is to assess for active tuberculosis disease. Obtaining a chest x-ray is critical in this context. A chest x-ray helps to visualize any active pulmonary disease that may necessitate further investigation and treatment. It can reveal classic signs of tuberculosis, such as cavitary lesions or infiltrates.

In contrast, other options range in relevance. While a complete blood count (CBC) could provide other health insights, it does not specifically address the potential for active tuberculosis. A sputum culture would be valuable if the chest x-ray indicated abnormalities consistent with TB, as it is used to confirm the diagnosis through the analysis of the respiratory secretions. Initiating TB treatment should only occur after confirming an active infection. Therefore, obtaining a chest x-ray is the most appropriate next step to determine the presence of active disease and guide further management.