What size of induration indicates a positive tuberculin test in a 16-year-old with no risk factors?

In the context of a tuberculin skin test, also known as the Mantoux test, the size of the induration that indicates a positive result can vary based on risk factors and the individual's demographics. For a 16-year-old with no additional risk factors for tuberculosis, an induration measuring 15 mm or more is considered a positive result.

The rationale for this threshold lies in the established guidelines for interpreting the tuberculin test. In general, the criteria are as follows:

• An induration of 5 mm or more is considered positive in immunocompromised individuals.

• An induration of 10 mm or more is considered positive in individuals with certain risk factors.

• A measurement of 15 mm is generally the threshold for those who are healthy and do not have additional risk factors.

Since the question specifies a 16-year-old with no risk factors, the 15 mm threshold is appropriate as it captures the response of a healthy individual to potential exposure to the tuberculosis bacterium, thereby indicating a positive result under these specific circumstances.