Willeke P.J. Franken1, Steven Thijsen2, Ron Wolterbeek3, John J.M. Bouwman2 , Hanane el Bannoudi1, Sandra V. Kik4,5, Jaap T. van Dissel1, Sandra M. Arend1


ABSTRACT


Background


T-SPOT.TB is a specific assay for the diagnosis of tuberculosis. The assay needs to be  performed with freshly isolated cells and interpretation requires training. T-SPOT.TB has  been used in various clinical-epidemiological settings, but so far no studies evaluated the  effect of inter-observer variation in test reading.

 Aim


 To evaluate variation between different observers in reading T-SPOT.TB results.


Materials & Methods


The study was nested within an ongoing cohort study, in which part of the T-SPOT.TB had  been performed with frozen material. Culture plates were read visually by four different  observers from two laboratories, and by two automated readers.


Results


Of 313 T-SPOT.TB assays, 235 were performed with fresh and 78 with frozen cells. No significant difference was found between results obtained with fresh or frozen cells. The percentage of positive results varied between readers by maximally 15%; 5/6 raters were within a 6% difference in positive results. Analysis of the observed inter-rater differences showed that some individuals systematically counted more spots. Because test interpretation includes subtraction of background values, this systematic variance had little influence on inter-individual differences.


Conclusion
The test result as positive or negative varied between independent raters, mainly due to samples with values around the cut-off. This warrants further study regarding determinants affecting the reading of T-SPOT.TB.

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A Rede Brasileira de Pesquisa em Tuberculose (REDE-TB) é uma Organização Não Governamental (ONG) de direito privado sem fins lucrativos, preocupada em auxiliar no desenvolvimento não só de novos medicamentos, novas vacinas, novos testes diagnósticos e novas estratégias de controle de TB, mas também na validação dessas inovações tecnológicas, antes de sua comercialização no país e/ou de sua implementação nos Programa de Controle de TB no País.


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