Comparing QuantiFERON-tuberculosis gold, T-SPOT tuberculosis and tuberculin skin test in HIV-infected individuals from a low prevalence tuberculosis country

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Abstract
To evaluate the interferon-gamma-releasing assays QuantiFERON-tuberculosis (TB) Gold and T-SPOT.TB in addition to tuberculin skin test (TST) for diagnosis of latent tuberculosis infection in HIV patients. Prospective cross-sectional study for asymptomatic HIV-infected outpatients from a large University hospital. Simultaneous performance of QuantiFERON-TB Gold, T-SPOT.TB and TST. Incidence and risk factors for a positive test reaction and the concordance (kappa) between the tests were investigated. Of 286 enrolled patients, 81% were men; median age was 44 years, the median CD4 cell count 408/microl (range 7-1510) with a median nadir of 126/microl (range 0-749). A number of patients (63.8%) had undetectable HIV RNA (<50 copies/ml). Both T-SPOT.TB and QuantiFERON-TB showed more positive test results than TST: 25.2 and 20.0% (P = 0.133) compared with 12.8% (P < 0.001 and P = 0.008, respectively). Agreement between T-SPOT.TB and TST (kappa = 0.201) respectively QuantiFERON-TB and TST (kappa = 0.335) was fair, but only poor between the serological assays (kappa = 0.146). T-SPOT.TB provided more indeterminate results than QuantiFERON-TB (8 vs. 1/256, P < 0.01). Patients with a positive QuantiFERON-TB result had higher median CD4 cell counts (457 vs. 405 cells/microl for patients with negative result, P = 0.044); the amount of released interferon-gamma correlated with CD4 cell counts (rho = 0.199; P < 0.002). T-SPOT.TB results were independent from CD4 cell counts. In HIV-infected patients from a low prevalence TB country, both interferon-gamma assays are more sensitive than TST, but seem to be less sensitive than in immunocompetent patients. The blood tests show poor agreement and differ in their dependence on the CD4 cell count.