A Mantoux test in a child with no risk factors is considered positive with a reaction of:

A Mantoux test in a child with no risk factors is considered positive with a reaction of:

• A. At least 5 mm induration
• B. At least 8 mm induration
• C. At least 10 mm induration
• D. At least 15 mm induration

Answer: (D)

A positive Mantoux reaction in a child with no risk factors is defined by an induration of 15 millimeters or more. The induration, not the redness, is measured 48 to 72 hours after injection. Using this higher cutoff helps avoid labeling children who are unlikely to have latent TB infection as positive, since smaller indurations can result from prior BCG vaccination or exposure to non-tuberculous mycobacteria. In groups with higher risk—such as recent contact with TB, immunocompromise, or birth in a high-prevalence country—a lower threshold (for example, 10 mm or 5 mm) is used because the pretest probability of true infection is higher. Thus, the 15 mm mark best fits a child with no risk factors.

A positive Mantoux reaction in a child with no risk factors is defined by an induration of 15 millimeters or more. The induration, not the redness, is measured 48 to 72 hours after injection. Using this higher cutoff helps avoid labeling children who are unlikely to have latent TB infection as positive, since smaller indurations can result from prior BCG vaccination or exposure to non-tuberculous mycobacteria. In groups with higher risk—such as recent contact with TB, immunocompromise, or birth in a high-prevalence country—a lower threshold (for example, 10 mm or 5 mm) is used because the pretest probability of true infection is higher. Thus, the 15 mm mark best fits a child with no risk factors.