A new study that shows wide variation in the results of commercially-available assays used to detect antinuclear antibodies in people with established systemic lupus erythematosus has thrown into question the assays’ role in determining eligibility for trials as well as their role in clinical practice.

The study’s findings of negative results ranging from 5% to 22% of samples with three different commercially available immunofluorescence assays (IFAs), one ELISA assay, and one bead-based multiplex assay reveal that “ANA negativity can occur in established lupus not infrequently [and] the use of certain ANA assays could affect the frequency of screen failures in the trial setting as well as the eventual utilization of an agent if approved for serologically active patients,” David S. Pisetsky, MD, PhD , of Duke University, Durham, N.C., and his associates wrote in their report published in Annals of the Rheumatic Diseases .

In addition, they noted that “in the routine clinical setting, these findings indicate that the serological evaluation of lupus could be misleading depending on the kit used, an issue not well appreciated by clinicians despite reports in the literature.”

People with systemic lupus erythematosus (SLE) have been thought to be “almost invariably” ANA positive, leaving the usual performance of testing to initial evaluation but not later unless a patient seeks care from another provider or undergoes screening to determine eligibility for entry into clinical trials of new therapeutic agents even though existing assays are not validated for this purpose. This practice first began with the development of the monoclonal antibody belimumab (Benlysta). Phase 2 trials showed that patients who were serologically positive (ANA and/or anti-DNA) were more likely to respond to the agent. Phase 3 trials that followed enrolled only serological positive patients and met their endpoints, the investigators explained.

“In view of the increasing use of ANA for determining trial eligibility, an explanation of these observations is important since it can impact both trial enrollment and eventual utilization of a product approved for autoantibody positive patients,” they wrote.

The research team assessed sera from 103 SLE patients using three different IFAs, an ELISA assay, and a bead-based multiplex assay. Results showed that the frequency of ANA positivity varied markedly depending on the assay platform and kit used. Among the IFA kits, negative results varied from 5 to 23 of 103 samples (4.9%-22.3%), although some samples had indeterminate results. Negative results occurred in 12 (11.7%) of the ELISA samples and in 14 (13.6%) of the multiplex assay samples.

Patients who consistently tested ANA positive in all assays differed from those who had discordant results among assays based on their likelihood of historical anti-double stranded DNA positivity and low levels of C3 complement.

This difference may have implications for the use of assays to determine eligibility for entry into a trial, the investigators noted. They advised that clinical trial protocols should specify which kits can be used to determine eligibility and how they characteristically perform, particularly for patients with established disease.

“Since the ANA assay used for screening is often not specified in protocols, the selection of a kit could lead to as much as a 17% change in the number of screen failures,” they speculated. “Correspondingly, for products approved for serologically active SLE, the use of certain assays could determine whether a patient meets criteria for its use.”

Future studies are needed to identify the assays that are most informative as theranostic biomarkers. Questions also remain over whether ANA positivity should be a criterion for trial entry in people with SLE of long duration, and if people with seronegative disease should be studied separately, they added.

The Lupus Industry Council supported the study. No authors had conflicts of interest to declare.

SOURCE: Pisetsky D et al. Ann Rheum Dis. 2018 Feb 9. doi: 10.1136/annrheumdis-2017-212599


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