Indeterminate test results of T-SPOT.TB performed under routine field conditions.
Interferon-gamma release assays for the diagnosis of tuberculosis (TB) can give indeterminate results. The prevalence of indeterminate test results (ITRs) among T-SPOT.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 (>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-SPOT.TB under routine conditions were infrequent and more common in individuals aged >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.
Beffa
P
P
Dept of Ambulatory Care and Community Medicine, University of Lausanne, Rue du Bugnon 44, 1011 Lausanne, Switzerland.
Zellweger
A
A
Janssens
J-P
JP
Wrighton-Smith
P
P
Zellweger
J-P
JP
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007371:Interferon-gamma / Q000032:analysis / Q000378:metabolism*; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D011933:Reagent Kits, Diagnostic / Q000382:microbiology*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000378:metabolism / Q000382:microbiology*; D014376:Tuberculosis / Q000097:blood / Q000175:diagnosis*
D011933:Reagent Kits, Diagnostic; D007371:Interferon-gamma