Is it necessary to request testing for antibodies against extractable nuclear antigens in case of antinuclear antibody negativity?

Background: Inappropriate or unnecessary test requests are one of the reasons for the increase in laboratory utilization. We aimed to investigate the frequency of simultaneous antinuclear antibody (ANA) and extractable nuclear antigens (ENA) test orders and to investigate whether ENA test ordering is necessary in the presence of negative ANA in terms of criteria for rational test selection.

Methods: We examined 2 years of data from a Turkish tertiary hospital in this retrospective cohort analysis. ANA and other autoimmune test data and clinical information of all patients with a negative ANA but positive ENA were obtained from the hospital record system.

Results: 32,800 patients had 37,584 ANA tests between January 2019 and January 2021. 4136 patients were tested for ANA simultaneously. Out of 2279 negative ANA tests, 371 (16.2%) were positive for ENA. Out of 307 individuals with negative ANA but positive ENA and clinical information, 23 were newly diagnosed with ANA-associated rheumatic disease (AARD), a 7.4% positive predictive value. The most common autoantibody causing ANA/ENA discordant results was anti-Ro52 (61 [19.9%]), followed by anti-DFS70 (53 [17.3%] and anti Jo-1 (48 [15.6%]).

Conclusions: The results of our study support proposals to reduce ENA testing after a negative ANA test and gradually increase it after a positive test or clinical indication. It will eliminate inaccurate test requests, expenditures, and unnecessary patient assessments.