European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-64
INTERPRETATION OF POSITIVE M. tuberculosis ANTIGEN
SPECIFIC IFNΓ RELEASE ASSAYS IN TUBERCULOSIS DIAGNOSIS
Greib Carine 1 , Lazaro, Estibaliz 1 , Viallard, Jean-François 1 , Pellegrin, Jean-Luc 1 , Maugein, Jeanne 2
1 - Medecine Interne et Maladies Infectieuses CHU Haut-Leveque Bordeaux
2 - Laboratoire de bactériologie, CHU Haut-Leveque Bordeaux
QuantiFERON-TB Gold in tube test is an accurate test to detect immune responses against active Mycobacterium
tuberculosis infection (TB) and has the advantage to eliminate false positive outcomes due to BCG vaccination
and non-TB mycobacteria. Howevever there are still some false positive tests which remain unexplained.
In this study we aimed to focus on the prevalence and the potential explanation of false positive tests among a cohort of
patients accurately screened without TB.
A total of 250 adults patients with suspicion of active tuberculosis were enrolled in this study between January 2007 and
December 2008.
Among them, 88 had positive result in accordance with manufactured interpretation (Nil ≤ 8I/mL, TB antigen ≥ 0.35 IU/
mL and ≥ 25% of Nil value). For 28 patients, tuberculosis was confirmed by culture of Mycobacterium tuberculosis in 26
cases and Mycobacterium bovis in 2 cases. For 9 patients, diagnosis of active tuberculosis was made according to a clinical
and paraclinical body of arguments. For 10 patients without active tuberculosis, we could suspect a technical mistake to
explain the positive result of the test (TB antigen near 0.35IU/mL for 4 patients and mitogen < 0.5IU/mL for the 6 others).
Among the other 41 patients out of 88 with a positive test without any argument for TB, we found that
12 had previous diagnosis of active tuberculosis in the past and 13 came from tuberculosis endemic areas.
Finally, 16 positives results out of 88 (18 %) remain without explanation. Errors of diagnosis, bias in collection of medical
information (previous or latent tuberculosis infection), or technical mistakes could be possible reasons.
In conclusion, quantiFERON-TB is a useful tool for diagnosis of active TB. However the results have to be carefully analysed
according to the high rate of false positive diagnosed in this study.
136 ESM 2009