IP-10 has potential as a diagnostic marker for infection with Mycobacterium tuberculosis, with comparable accuracy to QuantiFERON-TB Gold In-Tube test (QFT-IT). The aims were to assess the sensitivity and specificity of IP-10, and to evaluate the impact of co-morbidity on IP-10 and QFT-IT. 168 cases with active TB, 101 healthy controls and 175 non-TB patients were included. IP-10 and IFN-γ were measured in plasma of QFT-IT stimulated whole blood and analyzed using previously determined algorithms. A subgroup of 48 patients and 70 healthy controls was tested in parallel with T-SPOT.TB IP-10 and QFT-IT had comparable accuracy. Sensitivity was 81% and 84% with a specificity of 97% and 100%, respectively. Combining IP-10 and QFT-IT improved sensitivity to 87% (p < 0.0005), with a specificity of 97%. T-SPOT.TB was more sensitive than QFT-IT, but not IP-10. Among non-TB patients IP-10 had a higher rate of positive responders (35% vs 27%, p < 0.02) and for both tests a positive response was associated with relevant risk factors. IFN-γ but not IP-10 responses to mitogen stimulation were reduced in patients with TB and non-TB infection. This study confirms and validates previous findings and adds substance to IP-10 as a novel diagnostic marker for infection with M. tuberculosis. IP-10 appeared less influenced by infections other than TB; further studies are needed to test the clinical impact of these findings.
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