Professional and Linguistic Assessments Board (PLAB) Practice Exam

What size reaction indicates a positive Mantoux test for tuberculosis?

1. 6 mm or more

2. 4 mm or more

3. 8 mm or more

4. 10 mm or more

The correct answer is: 6 mm or more

The size of the induration that indicates a positive Mantoux test for tuberculosis primarily depends on the patient's risk factors and health status. For individuals who are considered at low risk for tuberculosis (for example, those with no known exposure or risk factors), a size of 10 mm or more is typically used to indicate a positive result. However, for individuals with specific risk factors—such as those who are immunocompromised, have recent contact with a TB case, or have a history of previous TB infection—a reaction of 5 mm or more could be classified as positive. In this question, the focus appears to be on a general context where a result of 6 mm or more can be interpreted as significant, especially in certain populations or within specific testing frameworks where even a smaller reaction might warrant further investigation. Nonetheless, determining the significance of the reaction requires consideration of the individual patient's context and background. Therefore, understanding the Mantoux test's interpretation is essential, as it highlights the importance of clinical judgement in evaluating the size of the induration based on various risk factors in the population being tested.