Low Conversion Rate of Quantiferon-TB Test in TNF Inhibitor-Treated Patients

An extremely low proportion of tumor necrosis factor (TNF) inhibitor-treated patients (0.4%) have experienced conversion in tuberculosis (TB) status based on Quantiferon-TB Gold In-Tube (QFT-GIT) tests, according to the results of a single-center, retrospective cohort study conducted at the University of Iowa Hospitals and Clinics and published in the Journal of the American Academy of Dermatology.

The investigators sought to determine the rate of conversion of QFT-GIT tests in patients receiving anti-TNF therapy. All patients who had been seen at the University of Iowa Hospitals and Clinics from January 2009 through November 2017, had received ≥2 interpretable QFT-GIT tests, and had a prescription history of taking a TNF inhibitor (ie, adalimumab, etanercept, infliximab, certolizumab, or golimumab) were evaluated.

A total of 265 patients with negative baseline TB screening were enrolled in the study. Median patient age was 42 years (interquartile range, 31-57 years); 52.1% of the participants were women. According to prescribing specialty, 43% (114 of 265) of patients were seen by dermatologists, 34.3% (91 of 265) by gastroenterologists, and 22.6% (60 of 265) by rheumatologists. Among the indications for TNF inhibitor therapy were psoriasis (37.7%; 100 of 265 patients), inflammatory bowel disease (34.3%; 91 of 265 patients), and inflammatory arthritis (20.8%; 55 of 265 patients). Median duration of anti-TNF treatment was 3.5 years (interquartile range, 1.9-5.8 years), and median duration between TB tests was 1.3 years (interquartile range, 1.0-2.0 years).

Among 265 enrolled participants, only 1 patent (0.4%) converted. This particular patient was asymptomatic, had no risk factors for TB, and had a negative chest X-ray. Although his test result might have been a false-positive, he was nonetheless treated for latent TB infection. No cases of active TB developed during or after anti-TNF therapy in patients who had a negative baseline TB test.

This appears to be the first multispecialty study performed in a low-prevalence area in the United States to investigate the rate of TB test conversion in patients receiving anti-TNF treatment. The researchers concluded that on the basis of the study findings, an extremely low proportion of patients (0.4%) converted during TNF inhibitor therapy, which translates to 1 in 1106.5 person-years. This suggests that serial TB testing in a low-risk population such as the one evaluated in this study might result in a high likelihood of false-positive test results, increased costs related to follow-up and unnecessary therapy, and increased likelihood of treatment-related adverse events. TB screening in low-prevalence areas thus should be limited to those with TB risk factors.

Reference

Chung J, Aronson AB, Srikantha R, Vogelgesang SA, Wanat KA. Low conversion rate of Quantiferon-TB Gold screening tests in patients treated with tumor necrosis factor inhibitors: a retrospective cohort study identifying an important practice gap [published online March 26, 2018]. J Am Acad Dermatol. doi: 10.1016/j.jaad.2018.03.025