Background/Purpose: Baseline screening for tuberculosis (TB) with tuberculin skin testing (TST) and/or interferon-gamma release assays (IGRAs) is recommended for all rheumatic patients starting biologic DMARDs (bDMARDs). Spontaneous conversions (from negative to positive) and reversions (from positive to negative) of available tests have questioned the value of re-screening patients during therapy. The aim of this study was to assess the long-term conversion and reversion rates of TB screening tests (TST and one IGRA: T.SPOT-TB) during long term bDMARD treatment.

Methods: Prospective study of rheumatic patients with negative baseline TB screening (TST and T.SPOT-TB, LTBI-1) prior to TNFi initiation who were re-screened for a 2^nd (LTBI-2: 1.4 ± 0.6 years) and 3^rd time (LTBI-3: 6.9 ± 1.0 years) after the 1st screening. Data regarding patient and disease characteristics, treatment patterns as well as conversion and reversion rates at LTBI-2 and LTBI-3 were recorded.

Results: 50 patients were included in the study; 4 patients who were treated with isoniazid due to a positive testing at LTBI-2 were excluded and thus 46 patients were available for final analysis. Twenty-eight (61%) were women and the mean age at LTBI-3 was 58.9 ± 13.5 years. RA was the most common diagnosis (n=22, 48%), followed by AS (n=13, 28%), PsA (n=9, 20%) and other rheumatic disease (n=2, 4%), with a mean disease duration of 15.6 ± 10 years. Forty-three (93%) patients were still on bDMARDs at LTBI-3 [TNFi: n=24 (56%), non-TNFi: n=19, (44%)] while 35% were on csDMARDs (n=16) and 15% on corticosteroids (n=7, mean daily prednisone dose = 4.5 ± 1 mg). Only one patient reported possible TB exposure during follow-up. Twelve (26%) patients had history of BCG vaccination. During follow-up, 35 patients (76%) remained persistently negative with both tests at the 2 re-screenings (“non-converters”). Among the “converters” (n=11), 4 (9%) had a transient conversion to positivity at LTBI-2 (3 with TST and 1 with T.SPOT-TB) that reversed to negative at the 3^rd re-screening (“transient converters”), 5 (11%) had a late conversion to positivity (“late converters”) between the 2^nd and 3^rd re-screening (4 with TST and 1 with T.SPOT-TB) while only 2 (4%) were “persistent converters” (both with TST). There was no statistically significant difference between “converters” (n=11) and “non-converters” (n=35), with the exception of a higher non-RA diagnosis among “converters” (73%) compared to “non-converters” (46%, p=0.04). Among the 11 conversions/reversions, 9 were observed with TST (20%) and 2 with T.SPOT-TB (4%); none of the patients developed TB during follow-up.

Conclusion: In a low-TB prevalence country, approximately one out of four rheumatic patients with negative TB screening at baseline displayed a positive TB screening test during long term biologic treatment (~7 years); most of the conversions/reversions were seen with TST than with the IGRA test (T.SPOT-TB). These data emphasize the need for large scale studies assessing the value of TB re-screening in this patient population.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-rates-of-conversion-and-reversion-of-tuberculosis-screening-assays-in-rheumatic-patients-during-long-term-biologic-treatment/