Journal Article

Tuberculin Skin Testing in Patients with HIV Infection: Limited Benefit of Reduced Cutoff Values

Frank G. Cobelens, Saidi M. Egwaga, Tessa Ginkel, Hemed Muwinge, Mecky I. Matee and Martien W. Borgdorff

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 43, issue 5, pages 634-639
Published in print September 2006 | ISSN: 1058-4838
Published online September 2006 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/506432
Tuberculin Skin Testing in Patients with HIV Infection: Limited Benefit of Reduced Cutoff Values

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Background. When determining eligibility for isoniazid preventive therapy of human immunodeficiency virus (HIV)–infected patients, the cutoff value of the tuberculin skin test (TST) is often reduced from an induration of 10 mm in diameter to one of 5 mm in diameter to compensate for loss of sensitivity. The effectiveness of this reduction depends on the underlying mechanism: a gradual decrease in skin test responsiveness with decreasing immunocompetence or an all-or-nothing switch to complete anergy. No published studies have assessed this directly in patients with tuberculosis.

Methods. We performed a cross-sectional study of TST responses and HIV infection among patients with sputum smear–positive pulmonary tuberculosis in 6 hospitals in Tanzania. Skin test anergy was defined as a TST reaction <2 mm in diameter.

Results. Of 991 patients with complete results, 451 (45.5%) had HIV infection. Anergy was observed in 111 (24.6%) of 451 HIV-infected patients and 18 (3.3%) of 540 HIV-uninfected patients (P < .001). The reaction size distributions among nonanergic HIV-infected and uninfected patients showed a limited difference (mean diameter ± standard deviation, 15.9 ± 5.0 mm and 16.8 ± 3.8 mm, respectively; P = .048). The sensitivity of the TST among HIV-uninfected patients was 91.1% at a cutoff value of 10 mm and 95.2% at a cutoff value of 5 mm. The sensitivity of the TST among HIV-infected patients was 64.3% at a cutoff value of 10 mm and 71.2% at a cutoff value of 5 mm; the sensitivity of the TST was 67.6% and 74.5%, respectively, after adjustment for tuberculosis-specific anergy.

Conclusion. In subjects with tuberculosis disease and HIV infection, loss of TST sensitivity is predominantly attributable to anergy (i.e., an all-or-nothing phenomenon). The decrease in the proportion of false-negative TST results obtained by reducing the cutoff value from 10 mm to 5 mm is limited.

Journal Article.  3771 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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