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* = Presenting author

P189 Latent tuberculosis: Diagnostic value of QuantiFERON and genetic association to the SNP INFG+874 T/A

L. Kallel*, R. Ben Jemaa, N. Ben Mustapha, A. Laabidi, M. Ghermi, M. Serghini, M. Fekih, J. Boubaker, M. Sellami, A. Filali

Rabta Hospital, Gastroenterology A department, Tunis, Tunisia

Background

This study was conducted in patients with inflammatory bowel diseases (IBD) to evaluate the performance of Mycobacterium tuberculosis (Mtb) antigen-specific interferon gamma releasing assay (QuantiFERON®-TB Gold In-Tube) for the diagnosis of latent tuberculosis infection (LTBI) comparing to tuberculin skin test (TST), to assess the impact of immunomodulator (IM) treatment in their performances and to analyze whether IGRA positivity is related to genetic susceptibility by screening for INFG +874 (T/A) SNP.

Methods

TST by Mantoux method and QuantiFERON®-TB Gold In-Tube (QFT-GIT) in accordance with manufacturer's instructions, were prospectively performed in 100 consecutive IBD patients and 54 healthy individuals. The SNP genotyping was done by an ARMS-PCR technique.

Results

A better agreement was observed between test's Results in controls (k = 0.40) than in patients (k = 0.16). Results found by TST were more positive than those obtained by QFT-GIT and this was the case for both groups: controls [24.1% versus7.5%] and patients [14.3% versus 9.9%], respectively. Although QFT-GIT Results were unaffected by IM therapy, the mean mitogen response was reduced in immunosuppressed patients (8.06 UI/ml) when compared to the rest of patients and controls (12.70 UI/ml). Similarly, lesser TST positivity was observed in those under IM (9.8% versus 20.5%). Among the 12 QFT+ subjects, 10 (88.3%) had the susceptibility allele (A). Additionally, 6 of them were homozygote for this allele (AA).

Conclusion

Although IM weakens the immunity strength, QFT-GIT seems to be as previously described, more accurate for detecting LTBI's cases that would otherwise be missed using solely TST. In a large vaccinated population, QFT-GIT appears more reliable for excluding a false positive TST. Even though, the (INFG +874T/A) SNP has been frequently associated with active tuberculosis, it seems that this SNP can also be associated with the latent form. All these preliminary Results will be ascertained as long as the size of both groups is enlarged.