A better definition of the anti-DFS70 antibody screening by IIF methods.

Background: Anti-DFS70 antibodies have been recently included in a new testing algorithm for patients with suspicion of connective tissue diseases (CTDs). This algorithm enables to assess the probability of having a CTD in patients with a positive antinuclear antibodies (ANA) result. The aim of the study was to analyze the the inter-method agreement between three different HEp-2 cell substrates for anti-DFS70 detection, focusing on two novel IIF methods that assess the presence of monospecific anti-DFS70 antibodies.

Methods: Immunological and clinical records of 29 patients who were double positive for anti-DFS70 autoantibodies using chemiluminescence assay (CIA) and Immunoblot (IB) were studied. The IIF on HEp-2 cells were determined using slides from Inova Diagnostics, Euroimmun and Immco. The capability to detect isolated anti-DFS70 antibodies was compared using immunoadsorption on NOVA Lite HEp-2 Select (Inova Diagnostics) and the HEp-2 ELITE/DFS70 knockout test (Immco).

Results: The three substrates had very good sensitivity for detecting patients with anti-DFS staining pattern (93.1%, 79.3% and 72.4% for Euroimmun, Immco and Inova respectively). Most of the patients had full inhibition of DFS pattern (65.5%) by immunoabsorption test. Also, the 55.2% of the subjects were positive for monospecific DFS pattern using HEp-2 ELITE/DFS70 knockout test. However, the correlation between the full inhibition by immunoadsorption and the monospecific DFS pattern in knockout cells was very low (kappa: 0.22).

Conclusion: The evaluation of monospecific anti-DFS70 antibodies is clinically fundamental and challenging using traditional HEp-2 IIF. Results obtained in this study support the hypothesis that the lack of standardization across IIF kits along with the subjectivity of user interpretation among other factors contribute to the overall reduction in the agreement.