In a healthy child 4 years and older with no risk factors for TB, a Mantoux induration of 10 mm is interpreted as:

In a healthy child 4 years and older with no risk factors for TB, a Mantoux induration of 10 mm is interpreted as:

• A. Positive
• B. Negative
• C. Indeterminate
• D. Requires repeat test

Answer: (B)

The main idea is how to interpret a tuberculin skin test in the context of risk factors. For healthy children who have no TB risk factors, the cutoff for a positive Mantoux result is a 15 mm or larger induration. This child is 4 years old and lacks risk factors, so a 10 mm induration does not meet the threshold for positivity. Therefore the result is interpreted as negative, meaning no TB infection detected by this test at this time. Keep in mind that a negative result can occur even in some cases with TB exposure if margins allow, but in a healthy child without risk factors a 10 mm reading is not considered evidence of infection. If risk factors were present—such as close contact with someone with active TB, immunocompromising conditions, or immunosuppressive therapy—a smaller induration could be considered positive, but that’s not the situation here.

The main idea is how to interpret a tuberculin skin test in the context of risk factors. For healthy children who have no TB risk factors, the cutoff for a positive Mantoux result is a 15 mm or larger induration. This child is 4 years old and lacks risk factors, so a 10 mm induration does not meet the threshold for positivity. Therefore the result is interpreted as negative, meaning no TB infection detected by this test at this time.

Keep in mind that a negative result can occur even in some cases with TB exposure if margins allow, but in a healthy child without risk factors a 10 mm reading is not considered evidence of infection. If risk factors were present—such as close contact with someone with active TB, immunocompromising conditions, or immunosuppressive therapy—a smaller induration could be considered positive, but that’s not the situation here.