Antinuclear antibodies (ANAs) have long been considered an important marker in rheumatologic conditions, particularly for the diagnosis and classification of patients with systemic lupus erythematosus, but recent findings are raising new questions about their role.
“We’ve measured ANAs for a long time – it’s a very important test in rheumatology,”, explained in an interview.
However, even though this test has been around for decades, “some interesting things have developed around it that have made a lot of people, including me, take a second look,” said Dr. Pisetsky, professor of medicine and immunology at Duke University, Durham, N.C.
He elaborated on those recent findings, which relate to the findings of ANA negativity in patients with an established diagnosis of systemic lupus erythematosus (SLE) and to variability among ANA test kit findings, during a presentation at the Winter Rheumatology Symposium sponsored by the American College of Rheumatology.
“Screening of patients during clinical trials for new treatments of SLE suggest that a significant number of people with lupus – 20%-30%, in fact – are ANA negative despite disease activity at the time the test is done,” he said.
For example, unpublished (but recently submitted) data from a phase 2 trial looking at the efficacy and safety of an interleukin-6 monoclonal antibody for the treatment of SLE showed that 23.8% of baseline samples from 183 SLE patients with positive historical ANA and clinically active lupus prior to randomization were ANA negative.
A particular concern with respect to such findings is that ANA positivity is typically a criterion for entry into clinical trials of therapies for lupus and prescription of medications approved for active lupus, Dr. Pisetsky said.
“On the other hand, about 20% of otherwise healthy people – especially women – can be ANA positive, so it’s always been problematic as a screening test due to these false positives, but these new findings suggest that in lupus a real concern is false negatives,” he said. “It’s quite a surprise.”
The findings raise questions about whether ANA negativity in SLE reflects the natural history of the disease, an effect of treatments, or a problem with the assays.
It appears an important problem relates to test kit variability, he said.
“There are lots of different ANA test kits. Their performance characteristics are very different. The performance of ANA tests is much more variable than people realize,” he said, citing data from an analysis that he and his colleagues conducted using 103 samples from a cohort of patients with established SLE.
In that 2017 study, an ANA enzyme-linked immunosorbent assay showed an ANA-negativity rate of 11.7% with zero indeterminate tests, whereas three different test kits showed ANA-negativity rates of 22.3% (with 8.7% of samples reported as indeterminate), 9.7% (with another 9.7% indeterminate), and 4.9% (with another 1.9% indeterminate), respectively. Multiplex testing showed a 13.6% ANA-negativity rate and an indeterminate rate of 7.8% ().
Only one sample tested negative for ANA on all three test kits, and disagreement about ANA negativity occurred in one-third of the samples, he said.