gms | German Medical Science

Background: The detection of antinuclear autoantibodies by immunofluorescence (ANA-IFT) supports the diagnosis of many different autoimmune and rheumatological diseases (ARE). In combination with the detection of specific autoantibodies against known extracted nuclear antigens (ENA) ANAs have high diagnostic sensitivity and specificity. However, positive ANA-IFT may also occur in disease states not related to ARE and even in healthy individuals. Especially in the latter group this may lead to unnecessary and repeated hospital visits, as well as avoidable diagnostic and therapeutic interventions. Anti-DFS70 autoantibodies were introduced as a biomarker for the exclusion of ARE in ANA-IFT + patients without additional ENAs and non-specific clinical history. Our aim was to evaluate if the diagnostic pathway for suspected or established ARE patients in our center benefits from the addition of anti-DFS70 autoantibodies to an existing ENA test profile.

Methods: Serum from patients was tested for anti-DFS70 autoantibodies by the ANA-Profil 3 plus DFS70 line blot (Euroimmun, Lübeck Germany).

Results: In 2017 the Freiburg university rheumatology center tested 671 patients, referred to for diagnosis or follow-up of ARE, for anti-DFS70 and 126 patients were found positive. Descriptive statistics of the anti-DFS70 positive vs negative cohorts are summarized in table 1. Of the 126 anti-DFS70 positive patients, 53 (42%) had one or more additional ENAs positively tested (4 snRNP/Sm,1 Sm,15 SS-A/Ro,15 Ro-52,2 SS-B/La,4 Scl-70,8 PM-Scl,2 PM-Scl75,1 SRP,2 Ku,1 Jo-1,4 Centromer,2 PCNA,2 Nukleosomes,9 Histones,1 ribos-P-Prot,2 AMA-M2,6 ds-DNA) and 3 (2%) patients had anti-DFS70 in conjunction with anti CCP autoantibodies. 70 (56%) patients were tested single positive for anti-DFS70. 81 (64%) of anti-DFS70 positive patients either had an established diagnosis of ARE or were newly diagnosed with ARE based on clinical criteria and laboratory results. The majority of these patients had additional ENAs or other autoantibodies tested positive, as described above. A diagnosis of ARE was excluded or revised with help of the anti-DFS70 result in 45 (36%) patients, all of these were anti-DFS70 positive only. In 10 of these patients (20%) preexisting therapies were discontinued (9 Hydroxychloroquin, 1 MTX/sulfasalazine).

Conclusion: We found a high added diagnostical value of anti-DFS70 autoantibodies testing, since they were helpful to rule out or revise a previously suspected diagnosis of ARE in more than a third all patients tested anti-DFS70 positive at our center. However, patients referred to a university rheumatology center are a highly selected cohort and have a higher probability being finally diagnosed with ARE, and thus consideration of clinical criteria and thorough testing for additional autoantibodies is recommended in such a setting since also many patients with confirmed ARE will test positive for anti-DFS70.