I am seeing an increasing number of patients who relate a past positive tuberculin skin test (TST) but were never treated with isoniazid (INH) prophylaxis. Before initiating INH treatment in an older patient with a remote history, would it be prudent to replant another TST or obtain a QuantiFERON-TB Gold test for confirmation? Is there any risk in replanting a TST many years after a possible positive TST?—TERRENCE STONE, PA-C, Chesapeake, Va.

Repeating the TST in a person with a previous positive result carries a risk of swelling and redness of the arm. If the positive TST occurred many years ago, reactivity may wane. While this does reduce the risk, it would be prudent to perform the Mycobacterium-specific interferon-gamma release assay (IGRA) instead of the TST. If your patient population includes foreign-born individuals, the IGRA will also separate out those who reacted to the TST because of previous BCG administration. A recent study found the IGRA outperformed the TST in sensitivity and specificity (Chest. 2009;135:1010-1018).—JoAnn Deasy, PA-C, MPH (140-4)

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