Poor concordance between interferon-gamma release assays and tuberculin skin tests in diagnosis of latent tuberculosis infection among HIV-infected individuals

Background: A new generation of diagnostic tests, the
interferon-gamma release assays (IGRAs), have been developed for
the detection of latent tuberculosis infection (LTBI). Limited data
are available on their use in HIV-infected persons. Methods: A
cross-sectional study was carried out at 2 HIV clinics in Atlanta
to assess the utility of two IGRA tests (T-SPOT. TB [TSPOT] and
QuantiFERON-TB Gold in Tube [QFT-3G]) compared to the tuberculin
skin test (TST). Results: 336 HIV-infected persons were enrolled.
Median CD4 count was 335 cells/mu l and median HIV viral load was
400 copies/ml. Overall, 27 patients (8.0%) had at least 1 positive
diagnostic test for LTBI: 7 (2.1%) had a positive TST; 9 (2.7%) a
positive QFT-3G; and 14 (4.2%) a positive TSPOT. Agreement between
the 3 diagnostic tests was poor: TST and TSPOT, [kappa = 0.16, 95%
CI (-0.06, 0.39)], TST and QFT-3G [kappa = 0.23, 95% CI (-0.05,
0.51)], QFT-3G and TSPOT [kappa = 0.06, 95% CI (-0.1, 0.2)]. An
indeterminate test result occurred among 6 (1.8%) of QFT-3G and 47
(14%) of TSPOT tests. In multivariate analysis, patients with a CD4
= 200 cells/mu l were significantly more likely to have an
indeterminate result [ OR = 3.6, 95% CI (1.9, 6.8)]. Conclusion: We
found a low prevalence of LTBI and poor concordance between all 3
diagnostic tests. Indeterminate test results were more likely at
CD4 counts