The sensitivity of the PPD test varies, however, from 96% in the general population,(3) to 59% in the population infected with HIV,(4) to only 50% in critically ill patients with disseminated tuberculosis.
There is ongoing controversy concerning the most reliable method for separating a negative PPD test due to nontuberculous infection from negative tuberculin reactivity secondary to cutaneous anergy.
The remaining 185 either did not have a PPD test performed or did not meet inclusion criteria.
If the PPD test is negative, the question frequently facing the clinician is: is the patient free of tuberculosis infection, or is the PPD test result a false negative secondary to cutaneous anergy?
It does suggest, however, the selection of Candida, mumps, and histoplasmin or tetanus as adequate and reasonable choices when attempting to control for anergy in the face of a negative PPD test reaction.
Furthermore, they suggest that the mumber of millimeters of induration required for a positive PPD test result in other patients should be determined by the patient's risk of acquiring tuberculosis.
In spite of the CDC's recommendation, many health care workers who administer and interpret PPD tests believe that a BCG vaccination always results in a positive PPD test.
8] Thus, a positive PPD test in an immigrant or farmworker is more significant than in almost any other population group.
There is some logic to the proposition that BCG produces a positive PPD test result.
11] This is the basis for the 10-mm cutofffor positivity ofthe PPD test, since exposure to MOTTs typically results in a PPD test reaction of 3 to 8 mm.
In screening patients for tuberculosis, it is essential that clinicians consider all positive PPDs as evidence of possible primary infection and clinically evaluate patients with positive PPD test results regardless of BCG vaccination history or the presence of a BCG scar.