HIV/AIDS & Tuberculosis: Tuberculin skin testing sensitivity reduced in patients with HIV infection

AIDSWEEKLY Plus; Monday, October 23, 2006
Staff Medical Writers

"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," scientists in the Netherlands report.

According to the authors, "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 less than or equal to2 mm in diameter. 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<0.001). 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=0.048).

"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," wrote F.G. Cobelens and colleagues at KNCV Tuberculosis Foundation in The Hague.

Researchers continued, "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."

"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," Cobelens concluded.

Cobelens and colleagues published their study in Clinical Infectious Diseases (Tuberculin skin testing in patients with HIV infection: Limited benefit of reduced cutoff values. Clin Infect Dis. 2006 Sep 1;43(5):634-9).

For additional information, contact F.G. Cobelens, KNCV TB Foundation, Pk Str 17, NL-2514 JD The Hague, Netherlands.

The publisher's contact information for the journal Clinical Infectious Diseases is: University Chicago Press, 1427 E 60th St., Chicago, IL 60637-2954, USA.

Keywords: JD The Hague, Netherlands, HIV/AIDS, False-Negative Test, Tuberculin Skin Test, Anergy, Test Sensitivity.

This article was prepared by AIDS Weekly editors from staff and other reports.

Reference

Cobelens FG, Egwaga SM, van Ginkel T, et al., “Tuberculin skin testing in patients with HIV infection: limited benefit of reduced cutoff values”, Clin Infect Dis. 2006 Sep 1;43(5):634-9.

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