Background/Purpose:

Mycobacterium tuberculosis (MTb) screening is routine for clinical trial protocols, & authorization for immunomodulators use by health insurances. Real world data is needed to guide clinicians and researchers in appropriate test choice. The two interferon gamma release assays (IGRAs) available to screen for MTb, QuantiFERON TB Fold In-Tube test (QFT-G) & SPOT TB (T-Spot), rely on an uncompromised immune system. Both, however, have a “+,” “-,” & “indeterminate (IND)” or in TSpot, “borderline” result. IND or borderline values have been theorized to result from an immunocompromised state, but the literature varies with regard to the effect of immunomodulation, particularly with corticosteroids, disease-modifying anti-rheumatic medications (DMARDs) and biologic response modifiers (BRMs)

Methods: The Center for Rheumatology and Bone Research (CRBR) obtained IRB review / waiver to conduct a retrospective chart review from 2014 to 2016. CRBR focused on care provided by Arthritis and Rheumatism Associates P.C. regarding medication use at the time of an IGRA. Data included IGRA type, test result (“+”, “-” & IND/borderline), & medication use. Medications were divided by corticosteroid (prednisone or methylprednisolone), DMARD use (including but not limited to hydroxychloroquine, sulfasalazine, MTX, azathioprine, leflunomide, cyclosporine) and exposure to a BRM (aka anti-TNFa therapy [such as etanercept, adalimumab, infliximab, certolizumab, golimumab], tocilizimab, abatacept rituximab and tofacitinib). A medication was considered active at the time of the laboratory if there were evidence of use within 1 month of testing. Statistical Analysis was performed using a student’s z-test as well as Chi-square analysis.

Results:

A total of 796 IGRAs were reported. There were 722 QTF-G tests and 74 Tspot drawn. Negative QTF-G values occurred in 643/722 (89%), equally distributed between those on & off immunomodulators. Positive QTF-G values occurred in 41/722 (5.6%), equally distributed between those on & off immunomodulators. IND QFT-G occurred in 38/722 (5.9%); the distribution was imbalanced. IND QTF-G occurred in 24/38 (63 %) on immunomodulators while IND QTF-G occurred in 14/38 (37%) with p=0.0087. IND QTF-G were more likely to occur during corticosteroid + DMARD / BRM treatment, occurring in 19/38 (50%) vs.DMARD ± BRM without corticosteroid, which occurred in 5/38 (13%) with p<0.025. This effect was not seen in non-steroid DMARD or non-steroid BRM treated cohort. This effect was not observed in the Tspot cohort, as IND / border line values occurred in 1/74 on immunomodulators while 2/72 subjects were not exposed to immunomodulators.

Conclusion:

Our cohort demonstrated positive, negative and IND rate similar to other published studies. However, our large QTF-G cohort demonstrated a statistically significant difference in IND values while taking immunomodulators, largely related to steroid exposure. Our smaller Tspot cohort did not demonstrate this effect, but this may have related to the cohort size. Further study to guide IGRA choice is warranted, but clinicians should consider Tspot over QTF-G when the subject is exposed to corticosteroid within a month of testing.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/real-world-igra-testing-in-rheumatology-practice/