A 70-year-old African American woman comes as a new patient to request clearance for her job as a day-care worker. She reports that she underwent partial lung resection and thoracoplasty to treat pulmonary TB in 1953, but she never received anti-TB therapy. We have no medical records. The patient declines purified protein derivative (PPD) testing, saying that previous results have been positive, but chest x-ray is always negative. Should I skip the PPD and just do a chest x-ray? If I do the PPD test and the induration is >22 mm, should I treat this patient as having latent TB?—Sunil Modi, MD, Johnstown, Pa.

Although the resection might have been effective, most experts would consider this patient to have latent TB. Confirm her latent status by ordering QuantiFERON-TB Gold (QFT-G) testing from whole blood. According to CDC guidelines released in 2005, the QFT-G can be used in all settings where PPD (now referred to as a “tuberculin skin test” [TST]) had been used previously (MMWR Recomm Rep. 2005 Dec 16;54[RR-15]:49-55. Available at www.cdc.gov /mmwr/preview/mmwrhtml/rr5415a4.htm. Accessed August 13, 2009). If the QFT-G is also positive, you can offer the patient nine months of isoniazid prophylaxis, emphasizing that she has up to a 20% lifetime risk of developing reactivation disease (N Engl J Med. 2004;350:2060-2067. Available at content.nejm.org/cgi/content /full/350/20/2060. Accessed August 13, 2009).—Cedric W. Spak, MD, MPH (131-13)