The diameter of induration (not erythema) is measured 48-72 hours after administration
of the PPD. A test is considered positive at
> 5 mm, > 10 mm, or > 15 mm depending on the patient.
> 5 mm: known or suspected HIV infection close contacts patients with
suggestive chest x-ray IV drug users with unknown HIV status
> 10 mm HIV negative IV drug users patients with underlying medical conditions
foreign born underserved, low income populations patients in long term care
facilities children < 4 years old healthcare workers that treat MTB patients
> 15 mm persons with no known risk factor for MTB
Management of a Positive Skin Test
Persons who are < 35 years of age should receive prophylaxis with Isoniazide
(INH) for 6 months unless they are at significant risk for an adverse reaction,
or they were exposed to INH resistant tuberculosis (in this case, prophylax
with rifampin).
