How to Boost the Accuracy of TB Testing in the Elderly

It struck me when reading Dr Thomas Petty's "PulmonaryQ&A" on when to treat latent tuberculosis (TB) infections(CONSULTANT, January 2003, page 48) that it is importantto remind clinicians how misleading tuberculin testingin the elderly can be if the 2-step testing procedure is notfollowed. Because of waning immunologic response, olderpatients may not have a positive reaction to an initial purifiedprotein derivative (PPD) test if they have not been giventhe test in recent years. Thus, such patients should be givena "booster" PPD test approximately 1 week later to ensurean accurate reading. When this is not done, a second testseveral weeks or months later may demonstrate a positiveresponse, and the patient may be incorrectly identified as a"recent converter" with active infection--when in fact theprevious PPD test simply "boosted" the immune response ina remotely infected person.The CDC provide very specific guidelines for 2-steptuberculin testing, and many health care employers nowrequire 2-step testing to more accurately evaluate employeeTB status.
---- Linda P. Whiteley, ARPN, BC, FNP
Holyoke, Mass
You make an important point about the "boostereffect" being misinterpreted as a PPD conversion.A true conversion indicates infection andcalls for anti-TB chemotherapy. A booster effectdoes not. There is no scientific basis for treatingolder persons with remote infection.
---- Thomas L. Petty, MD
Professor of Medicine
University of Colorado
Denver