Diagnosis of M. tuberculosis Infection Among HIV-Infected Persons
The Mantoux-method TST, with 5 TU of purified protein derivative, is used to diagnose M. tuberculosis infection. A TST reaction size of greater than or equal to 5 mm of induration is considered positive (i.e., indicative of M. tuberculosis infection) in persons who are infected with HIV. Persons with a TST reaction size of less than 5 mm but with a history of exposure to TB also could be infected with M. tuberculosis; this possibility should be investigated (157). Whenever M. tuberculosis infection is suspected in a patient, an evaluation to rule out active TB and assess the need for preventive therapy should be conducted (see Box 3(Table_B3)). This evaluation should include HIV counseling and testing for persons whose HIV status is unknown but who are at risk for HIV infection.

Tuberculin Skin Testing Among HIV-Infected Persons
A.I As soon as possible after HIV infection is diagnosed, all persons should receive a TST unless previously tested and found to be TST-positive.

A.II As soon as possible (ideally within 7 days) after learning of an exposure to a patient with infectious TB, all HIV-infected persons should be evaluated for TB and receive a TST, regardless of any previous TST results.

B.III TSTs should be conducted periodically for HIV-infected persons who are TST-negative on initial evaluation and who belong to populations with a substantial risk of exposure to M. tuberculosis (e.g., residents of prisons, jails, or homeless shelters).

C.III Some experts recommend repeat TSTs for HIV-infected persons who are TST-negative on initial evaluation and whose immune function is restored because of effective antiretroviral therapy.

C.I Because results of anergy testing in HIV-infected populations in the United States do not seem useful to clinicians making decisions about preventive therapy, anergy testing is no longer recommended as a routine component of TB screening among HIV-infected persons (157). However, some experts support the use of anergy testing to help guide individual decisions regarding preventive therapy, and some recommend that a TST be performed on patients previously classified as anergic if evidence indicates that these patients' immune systems have responded to therapy with antiretroviral drugs.

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