Prevalence and Clinical Significance of Anti-DFS70 in ANA Positive Patients Undergoing Routine ANA Testing in a New Zealand Public Hospital
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The presence of antinuclear antibodies (ANA) in serum is the hallmark diagnostic test for most Systemic Autoimmune Rheumatic Disease (SARD). Anti-dense fine speckled (DFS) 70 is an autoantibody that produces a characteristic dense fine speckled pattern in the ANA HEp-2 indirect immunofluorescence (IIF) assay. Its clinical significance is not yet clear however it has been reported that these antibodies are more prevalent in healthy individuals and non-SARD patients than in SARD patients. Thus it is has been proposed that the presence of anti-DFS70 antibodies could be used to eliminate a SARD diagnosis. To date, there is no published data as to whether this can be applied to a New Zealand population, nor what the prevalence of these antibodies are in a New Zealand population. The DFS IIF pattern can be difficult to identify and most New Zealand diagnostic laboratories do not specifically test for the autoantibody, therefore it is likely that its presence is currently being under-reported. The purpose of this research was to determine if New Zealand diagnostic laboratories should be specifically testing for anti-DFS70 antibodies and including the result in the laboratory report. Thus the principal objectives of this research were to (1) determine if current routine ANA testing methods are detecting anti-DFS70 antibodies, (2) determine the local prevalence of anti-DFS70 in ANA positive patients in a New Zealand public hospital population, (3) determine if the presence of anti-DFS70 is clinically significant in terms of a SARD diagnosis. Should anti-DFS70 prove to be a significant factor in terms of eliminating a SARD diagnosis, then a new ANA diagnostic algorithm would be proposed. Samples tested were a consecutive series of routine ANA positive patient samples at a general public hospital, consisting of 100 each of SARD and non-SARD patients. In order to ensure the likelihood of anti-DFS70 detection, two ANA detection methods were used (IIF and enzyme linked immunosorbent assay (ELISA)). All positive ANA samples were tested for anti-DFS70 by chemiluminescence immunoassay (CIA). Results showed that both the ANA IIF and ELISA assays are detecting anti-DFS70 antibodies. The prevalence of anti-DFS antibodies in SARD patients was 1% and in non-SARD patients was 7% and the difference between the two was statistically significant. In non-SARD patients anti-DFS70 was usually found in isolation with no other specific ANAs present. There was a significant difference in the prevalence of anti-DFS70 according to ethnicity but not by age or sex. In conclusion, the presence of anti-DFS70 antibodies, particularly when present alone without any other specific ANAs present, makes a SARD diagnosis highly unlikely. Therefore New Zealand diagnostic laboratories should be specifically testing for anti-DFS70 antibodies and including the result in the laboratory report. An appropriate interpretative comment should be included in the report as it is imperative that clinicians are aware of the significance of the anti-DFS70 result.