• "Anergy testing"-- The practice of making intradermal injections of common antigens (e.g. mumps, trichophyton) along with PPD as a "positive control" for PPD; the idea is that if a pt has a reaction to a control antigen they have intact delayed-hypersensitivity reaction and the absence of PPD reaction has more negative predictive value
  • Commonly done in HIV+ pts who are presumed to be more likely to be "anergic," i.e. incapable of mounting a reaction to an intradermal antigen. 
  • Positive anergy testing (i.e. reactions to the non-PPD intradermal antigens) and no tuberculin reaction is commonly taken to mean no TB infection
  • However, the validity of this approach has been called into question
  • In a study of HIV+ pts with active TB, 5-10% had negative tuberculin skin test but positive reaction to other antigens injected intradermally (JAMA 283:2003, 2000--abst)
  • In a study in 500 HIV+ pts with CD4 from < 200 to > 600 who underwent serial skin testing with PPD, mumps and candida, 36% were anergic to all at baseline; At one year, 1/3 of these anergic pts had positive reactions to either mumps or candida (associated with higher CD4 counts at baseline); 62 pts had initially positive reaction to PPD; 50 became negative, but 40% of those 50 still had reaction to mumps!  So, reaction to "anergy panel" and none to PPD doesn't necessarily mean pt is not infected with TB! But unknown how this applies if question of active TB is being considered (Am J. Resp. Crit. Care Med 153:1982, 1996)