“The focus of our work was to figure out what this [variability] was about, because the general belief is that almost everyone with lupus is ANA positive,” Dr. Pisetsky says.
Study Results & Implications
Dr. Pisetsky and colleagues studied sera from 103 patients from an Ohio State University cohort with established SLE who were historically ANA positive. The investigators screened the patients’ sera using three commercially available kits for IFA ANA determinations, as well as with an ELISA and a bead-based multiplex assay.
Results indicated marked variation in ANA positivity depending on the assay platform and kit used. Of the three IFA kits, 4.9–22.3% of the samples tested negative. Similarly, 12 samples tested negative with the ELISA assay, and 14 tested negative with the multiplex assays.
A couple of years ago Dr. Pisetsky and a different group of researchers studied 181 patients enrolled in a clinical trial for a new agent to treat SLE and found a wide variation in ANA negativity using five kits (0.6–27.6%). They presented their results at the 2016 ACR/ARHP Annual Meeting.
These results have implications for the clinical trial setting because of how researchers screen and enroll patients in trials of new therapeutic agents. “But the study has implications beyond the clinical trial setting,” Dr. Pisetsky says. “One of the important messages is that the so-called gold standard [IFA test] really has limitations, and there are significant differences in the detection of antibodies by kits produced by different manufacturers. So, the frequency of ANA negativity can vary.”
Beyond that, two implications are significant for practicing rheumatologists. “First, increasingly, the ANA is being used as an important criterion for classification of lupus,” Dr. Pisetsky says, which assumes nearly everyone with lupus is ANA positive. However, if the kits used for ANA testing are limited in their detection, it’s possible some patients who have lupus will test negative and potentially be misdiagnosed. Practicing rheumatologists may consider exploring different ANA assays used for diagnosis and possibly adapting other protocols.
“Second, in general, people are tested for ANA only at diagnosis—on initial presentation—and they’re not tested subsequently because of the belief that the information is already there,” Dr. Pisetsky says. Some patients may be retested if they change providers or care settings, but routinely, retesting for ANA is not usual in patients with lupus. “This study suggests that there may be reasons to retest.”
Retesting could become important as clinicians and researchers continue to investigate how patients respond to different treatments. The current approach of using ANA results to determine eligibility for clinical trials suggests differences exist in the responsiveness of patients with lupus to treatment depending on ANA status, although this depends on which kit is used for the ANA assay, Dr. Pisetsky says.
