CD4 and histoplasmosis: Elevated AST plus < 200 CD4 + cells/μL showed a sensitivity and NPV of 100%, with 0% false negatives, but the specificity was very low (11%) and the false positives very high (88%), implying that the combination of both tests are only useful to rule out histoplasmosis if the patient has > 200 CD4 + cells/μL and normal AST transaminase levels.