Diagnosing connective tissue diseases (CTDs) continues to challenge both clinicians and laboratorians. An influential guideline, developed by the European League Against Rheumatism and the American College of Rheumatology (EULAR/ACR) for systemic lupus erythematosus (SLE), has set the stage for standardizing the clinical diagnosis of SLE.
The 2019 EULAR/ACR guideline emphasizes the pivotal role of laboratory testing in diagnosing SLE. However, laboratories may encounter challenges when implementing the tests or providing interpretation for clinicians. Today’s scientific session, “Connective Tissue Diseases, Lupus, and dsDNA Testing: Updates in Diagnosis and Testing,” brings together three speakers to update attendees on the new guideline and to help laboratorians understand the limitations with the current tests for CTDs.
One important update from the 2019 guideline is the recommendation to have the antinuclear antibody (ANA) titer cutoff as ≥1:80 before further workup, making it an entry criterion for diagnosis. However, according to Rajeevan Selvaratnam, PhD, who will speak at this scientific session, “defining 1:80 as positive may assume that there is an acceptable level of standardization, which is not exactly true.” The challenges lie in different levels, “from variation in ANA reagents between manufacturers, to the technologists, who handle the sample manually,” says Selvaratnam.
So what is the solution? Selvaratnam will explain to attendees that the international guideline published in 2014 “suggested a more analytical approach to establish an ANA positivity cutoff based on a titer above the 95th percentile of the healthy reference population.” While this is ideal, establishing the positivity cutoff by individual laboratories is not an easy task.
One promising solution to this issue is the “movement to automated platforms for ANA by indirect fluorescent antibody (IFA) for increased standardization between laboratories,” says speaker Sarah Wheeler, PhD. She will detail how this can be achieved through automated sampling, reagent handing, processing, slide reading, and pattern interpretation, with reduced interventions or input from a clinical laboratorian.
However, even with automation, the “difference in substrates and positivity cutoffs continue to be sources of variability in ANA IFA,” says Wheeler. She notes that there are reports that ANA reactivity in the general population is increasing in the U.S. and U.K., further complicating determination of clinically relevant positivity cutoffs for ANA by IFA.
Ultimately, standardized materials and protocols should be developed. Guidelines are also needed for defining acceptable analytical characteristics that are able to translate into clinical performance in a consistent manner.
Similar challenges apply to another SLE-specific biomarker: antibodies against double stranded DNA (dsDNA). According to speaker Danyel Tacker, PhD, “the WHO developed a standard reference material (Wo/80) in 1985, but it has been exhausted since the 1990s.” A new material is desperately needed to improve comparability between laboratories using different assays.
Tacker and the other two speakers will use proficiency testing data, as well as a multicenter study that all three speakers took part in, to illustrate the lack of standardization of tests related to CTD, and the implication of this variability.
Differences in autoimmune testing can lead to differences in disease classification and diagnosis, particularly for SLE as the 2019 guidelines make laboratory testing an entry criterion for diagnosis. This scientific session prepares attendees for some potential challenges when implementing these assays in their own laboratories.