A healthy nurse in a suburban community hospital presents reporting she thinks she has a positive PPD from a skin test that had been placed 48 hours ago. She has no known specific TB exposures. What finding is indicative of a PPD test in this patient?
(a) Any amount of induration
(b) Induration > 5 mm
(c) Induration > 7.5 mm
(d) Induration > 10 mm
(e) Induration > 15 mm
The correct answer is E. Because the nurse works in a suburban area, with presumably low incidence of TB, and she has no history of immunocompromise, she is considered a lower risk category (despite working in health care facility)
The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) with needle bevel facing upwards intradermally such that there is a wheal of 6-10 mm diameter. The test must be read between 48 – 72 h of administration.
Classification of the Tuberculin Skin Test Reaction
|Induration > 5 mm is positive:
|Induration > 10 mm is positive:
-Recent immigrants (< 5 years) from high-prevalence countries
|Induration > 15 mm is positive:
-No known risk factors for TB.