High rate of indeterminate results of the QuantiFERON-TB Gold in-tube test, third generation, in patients with systemic vasculitis.

Objectives: To describe the frequency of QuantiFERON-TB Gold in-tube test® (QFT-GIT) indeterminate results due to no response to phytohaemagglutinin A stimulation in the control tube in vasculitis patients prior to immunosuppressant therapy; and to compare it with other groups of patients.
Methods: This was a single-centre, retrospective study. Patients and controls were included between 1 January 2008 and 31 December 2015. We assessed the rate of indeterminate results of the QFT-GIT in 38 patients with systemic vasculitis prior to any corticosteroid or immunosuppressant therapy, compared with 40 non-vasculitis patients with biological inflammatory syndrome, and 310 non-immunosuppressed patients matched for gender and age.
Results: Indeterminate results due to no response to phytohaemagglutinin A were more frequent in vasculitis patients (21.1%) compared with non-vasculitis patients with biological inflammatory syndrome (7.5%) (Fisher's exact test: P = 0.11) and to anonymized controls (7%) (P = 0.009). Responses to phytohaemagglutinin A were significantly lower in vasculitis patients compared with other groups (Kruskal-Wallis test: P < 0.0001) and compared with non-vasculitis patients with biological inflammatory syndrome (P = 0.0015). The multivariable analysis identified as independent predictors of an indeterminate result of the QFT-GIT: the presence of systemic vasculitis (odds ratio 9.64 [1.14-81.3], P = 0.037) and a high neutrophil-to-lymphocyte ratio (odds ratio 1.70 [1.21-2.37], P = 0.002). One patient with an indeterminate result of QFT-GIT developed active tuberculosis after one year of corticosteroid therapy for giant cell arteritis.
Conclusion: Our results question the reliability of QFT-GIT to rule out latent tuberculosis in vasculitis patients at diagnosis, prior to immunosuppressant therapy.
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