Diagnosis of tuberculosis infection in HIV-infected patients: an interferon-gamma assay versus tuberculin skin test

Abstract number: R2505

Casas S., Saumoy M., Robres P., Moure R., Andreu A., Alcaide F., Podzamczer D., Santín M.

Objectives: To compare the tuberculin skin test (TST) with a whole-blood interferon-gamma (IFN-g) assay in the diagnosis of tuberculosis infection (TBI) in HIV-infected patients.

Methods: Cross-sectional study of X HIV-infected patients evaluated at the HIV Unit of a third-level teaching hospital, between February and October 2007. Diagnosis of TBI was based on TB exposure, chest X-ray, two-step TST and IFN-g assay (QuantiFERON® TB Gold-in Tube, QFT). According to the manufacturer's instruction, QFT was considered as positive when the TB antigen minus negative control IFN-g production geqslant R: gt-or-equal, slanted0.35 UI/mL; an indeterminate result was defined as either a positive control IFN-g response of leqslant R: less-than-or-eq, slant0.5 UI/mL or a negative control IFN-g level of >8 UI/mL. A positive TST was defined as a geqslant R: gt-or-equal, slanted5 mm induration. Agreement between TST and QFT was assessed by the Cohen kappa (k) index.

Results: 39 patients were assessed for TBI, 69% men, with a mean age of 36 years. 49% were foreign-born. 54% had some TB risk factor and 39% were BCG vaccinated. 5% had a previous story of TBI. Mean CD4+ cell count was 376 (±279), 11 (28%) patients with CD4+ <200 cells/mL, and mean HIV-RNA was 118,569 copies/mL. 2 (5%) patients had a positive TST compared with 5 (13%) with QFT (p = 0.02). 3 patients had discordant results, all of them positive QFT/negative TST. 1/11 (6%) patients with CD4+ <200 showed a positive QFT but no one had positive TST. In the positive QFT group, some TB risk factor was presented in 60% (3/5) of cases but in no one in the positive TST group.)There were no indeterminate results due to low production of IFN-g in positive control tube. Overall agreement between the 2 tests was 92% (33/36, k=0.53, CI 95% 0.24–0.82).

Conclusions: These results suggest that QFT has higher sensitivity than TST for the diagnosis of TBI in HIV infected adults, particularly among those more immunosuppressed. TST and QFT agreement was moderate. There were not any indeterminate results due to low production of IFN-g even among patients with CD4+ <200.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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