TY - JOUR T1 - Indeterminate test results of T-SPOT<sup>TM</sup>.<em>TB</em> performed under routine field conditions JF - European Respiratory Journal JO - Eur Respir J SP - 842 LP - 846 DO - 10.1183/09031936.00117207 VL - 31 IS - 4 AU - P. Beffa AU - A. Zellweger AU - J-P. Janssens AU - P. Wrighton-Smith AU - J-P. Zellweger Y1 - 2008/04/01 UR - http://erj.ersjournals.com/content/31/4/842.abstract N2 - Interferon-γ release assays for the diagnosis of tuberculosis (TB) can give indeterminate results. The prevalence of indeterminate test results (ITRs) among T-SPOTTM.TB tests was assessed. A retrospective analysis of samples processed in 2005 was performed. ITRs were assessed by age, sex, immunosuppression, distance to the laboratory and season. A subgroup of tests performed for specific indications (contact tracing, migrants with positive tuberculin skin test, TB suspects and immunosuppression) were analysed separately. Of a total of 1,429 tests, 49 (3.4%) were indeterminate. ITRs were significantly associated with old age (&gt;75 versus 5–75 yrs; odds ratio (OR) 7.97, 95% confidence interval (CI) 3.968–15.438) and the season during which samples were transported (autumn and winter versus spring and summer; OR 3.47, 95% CI 1.753–7.514). The incidence of ITR was 302 (2.0%) among TB contacts, 75 (1.6%) among immigrants, 156 (3.0%) in TB suspects and 32 (3.0%) among immunosuppressed patients. Sex, young age and distance to the laboratory were not associated with the rate of ITR. Of the 13 tests with ITR that were repeated, 10 gave a clear positive or negative result. Indeterminate test results with T-SPOTTM.TB under routine conditions were infrequent and more common in individuals aged &gt;75 yrs than in children and younger adults. The incidence of indeterminate test results was low and similar among healthy tuberculosis contacts, immigrants with a positive tuberculin skin test, tuberculosis suspects and the immunosuppressed. The conditions of transportation may influence the incidence of indeterminate test results. ER -