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Hydroxychloroquine throws off Quantiferon-TB Gold results, study finds



QuantiFERON-TB Gold test results are much more likely to be indeterminate in patients with autoimmune skin diseases who are taking hydroxychloroquine, according to investigators from the University of Pennsylvania, Philadelphia.

Among 46 patients with lupus, dermatomyositis, or blistering diseases who had been on hydroxychloroquine within a year of testing, QuantiFERON-TB Gold (QFT-G) – the go-to TB test in many places – yielded indeterminate results in 37%. Meanwhile, just 9.6% of tests were indeterminate among 73 patients with those diseases who had not been on hydroxychloroquine (P less than .001). The findings could not be explained by concomitant use of prednisone and other immunosuppressives; there were no statistically significant differences between the groups. “This was shocking to us. We need to come up with a better screening test in this patient population,” said lead investigator Rebecca Gaffney, a research fellow at the University of Pennsylvania, and a medical student at Robert Wood Johnson Medical School, New Brunswick, NJ.*

Rebecca Gaffney, research fellow at University of Pennsylvania, Philadelphia, and medical student at New Jersey Medical School, Newark. M. Alexander Otto/MDedge News

Rebecca Gaffney

This is important because patients who fail first-line treatment with antimalarials need to be stepped up to immunosuppressives, but before that can happen, they have to be checked for latent TB. Indeterminate results can exclude patients from treatment with immunosuppressives and clinical trials, or, at the very least, delay treatment for repeat testing, chest x-rays, and infectious disease referrals, Ms. Gaffney said at the International Conference on Cutaneous Lupus Erythematosus.

It’s widely known that immunosuppressives interfere with QFT-G results, but antimalarials are considered immunomodulators, not immunosuppressives. The new study is probably the first to investigate the issue. The team is now pitting QFT-G against another TB blood test, the T-SPOT, in 100 patients to see if it’s a better option, in a trial that they expect to complete in 2018.

The investigators have a hunch that the T-SPOT might be better because, while QFT-G measures interferon-gamma concentrations in response to TB antigens, the T-SPOT “counts cells first to make sure you have a standard amount of cells, then looks at how many cells are releasing interferon-gamma,” Ms. Gaffney said, adding that “it seems like a more sensitive test,” especially for lymphocytopenic autoimmune patients. “We are really excited to see if there’s a better test for our patients, given all the clinical trials we do. We want to see what’s best, so there’s no barrier to receiving therapy.”

Subjects were around 50 years old on average, and the majority were women. Most were white, and about 20% were black.

There was no industry funding for the work, and Ms. Gaffney reported no disclosures.

*This article was updated on June 13. 2018.

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