In tuberculin testing, what induration size in a 16-year-old is considered positive?

In tuberculin testing, what induration size in a 16-year-old is considered positive?

• A. 10 mm
• B. 15 mm
• C. 20 mm
• D. 25 mm

Answer: (B)

In interpreting a tuberculin skin test, the size of the induration that counts as positive depends on the person’s risk factors. For a healthy 16-year-old with no significant risk factors, a positive result is indicated by an induration of 15 millimeters or more. This higher threshold helps limit false positives from prior BCG vaccination or other non-TB exposures. Keep in mind that thresholds change with risk. If there’s close contact with someone with active TB, immunocompromised status (such as HIV infection), or certain other risk factors, smaller indurations can be considered positive (for example, 5 mm or 10 mm, depending on the specific risk). The test is read 48–72 hours after administration, and only the induration diameter, not the surrounding erythema, is measured.

In interpreting a tuberculin skin test, the size of the induration that counts as positive depends on the person’s risk factors. For a healthy 16-year-old with no significant risk factors, a positive result is indicated by an induration of 15 millimeters or more. This higher threshold helps limit false positives from prior BCG vaccination or other non-TB exposures.

Keep in mind that thresholds change with risk. If there’s close contact with someone with active TB, immunocompromised status (such as HIV infection), or certain other risk factors, smaller indurations can be considered positive (for example, 5 mm or 10 mm, depending on the specific risk). The test is read 48–72 hours after administration, and only the induration diameter, not the surrounding erythema, is measured.