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Effect of Nucleic Acid Amplification for Mycobacterium tuberculosis on Clinical Decision Making in Suspected Extrapulmonary Tuberculosis^*

^* From the Departments of Medicine (Drs. Soylemez Wiener and Schluger) and Pathology (Dr. Della-Latta), Columbia University College of Physicians and Surgeons, New York, NY.

Correspondence to: Neil W. Schluger, MD, FCCP, Division of Pulmonary, Allergy, and Critical Care Medicine, Columbia Presbyterian Medical Center, 630 West 168th St, New York, NY 10032; e-mail: ns311{at}columbia.edu

Background: Laboratory-based studies have suggested the nucleic acid amplification test (NAAT) for Mycobacterium tuberculosis may be useful in diagnosing extrapulmonary tuberculosis. We sought to determine how clinicians in one hospital used results of the NAAT in clinical decision making in cases of suspected extrapulmonary tuberculosis.

Methods: We performed a retrospective analysis of all patients who underwent the NAAT on at least one nonsputum sample, excluding cerebrospinal fluid, from 1999 to 2001 in one large urban hospital. For these patients, we reviewed the hospital course, with particular attention to date of the NAAT and its influence on days treated with antituberculous medications and days to final diagnosis.

Results: Thirty-five patients with suspected tuberculosis who had undergone the NAAT on extrapulmonary specimens were identified. From three patients, NAAT results were nondiagnostic because of inhibitors, and they were excluded from the analysis, leaving 32 patients. Tuberculosis was ultimately diagnosed in 14 of these 32 patients. NAAT findings were positive in specimens from 12 of 14 patients with extrapulmonary tuberculosis and in 0 of 18 cases in which tuberculosis was excluded (sensitivity, 86%; specificity, 100%; positive predictive value, 100%; negative predictive value, 90%). In only 2 of 19 patients treated with antituberculous medications was the NAAT result used to determine the onset or discontinuation of therapy. In no instance was a negative NAAT result used by clinicians as definitive evidence that a patient did not have extrapulmonary tuberculosis; in all but one case, patients were continued on antituberculous therapy until final culture results were available.

Conclusions: The NAAT proved to be a sensitive and specific test for detection of M tuberculosis in extrapulmonary specimens but did not weigh heavily in clinical decision making at our hospital. Judicious use of these tests may improve the accuracy and speed of diagnosis of extrapulmonary tuberculosis, while helping to eliminate unnecessary antituberculous treatment in patients without tuberculosis.

Key Words: decision making • extrapulmonary tuberculosis • Mycobacterium tuberculosis • nucleic acid amplification testing