The presence of anti-cellular antibodies [1], commonly referred to as antinuclear antibodies (ANA), directed against intracellular antigens is a hallmark of ANA-associated rheumatic diseases (AARD) [2]. ANA are most commonly detected by the indirect immunofluorescence (IIF) assay on HEp-2 cell substrates [3]. However, not all ANA are associated with AARD thus complicating the interpretation and use of the test results [4]. Anti-dense fine speckled 70 (anti-DFS70) antibodies were initially identified as generating a specific ANA IIF pattern from a patient with interstitial cystitis [5], but were later associated with various other conditions (reviewed in [6]). The DFS pattern as detected by IIF on HEp-2 cells has been associated with several inflammatory diseases but is most commonly observed in individuals that do not have an AARD and even in apparently healthy individuals (HI). Consequently, the accurate identification and correct reporting of this IIF pattern is of utmost importance. This pattern has been recognized by several international study groups for the detection of ANA [1, 7, 8] and the DFS IIF pattern has recently been assigned the AC-02 nomenclature and designated as a competency level recognition pattern by the International Consensus on ANA Pattern (ICAP, http://www.anapatterns.org/) Committee.
With respect to the prognostic and long-term outcome of individuals with anti-DFS70 antibodies, it was reported that none of 40 HI with isolated anti-DFS70 reactivity developed an AARD within an average 4-year follow-up [9]. Therefore, it was suggested that the presence of isolated anti-DFS70 antibodies could be used to help to rule out a diagnosis of AARD including systemic lupus erythematosus (SLE), systemic sclerosis (SSc), inflammatory idiopathic myopathies (IIM), Sjögren’s syndrome (SjS) and mixed connective tissue disease (MCTD) [9-12]. In previous studies, it was found that anti-DFS70 antibodies are more prevalent in females than in males, a finding that is important since females are also predominately affected by AARD [10].
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Since ANA and related autoantibodies are generally considered useful biomarkers for AARD (which have low prevalences) and are included in the classification criteria for SLE [13], MCTD [14], SjS [15] and SSc [16], ANA testing on HEp-2 substrates outside a proper clinical framework may yield a sizable portion of ANA-positive individuals without consistent evidence of AARD. In this context, ANA testing may purportedly lead to inappropriate referrals to tertiary care specialists, as well as anxiety in patients and physicians alike [9] and, perhaps, inappropriate and potentially toxic therapies [17]. Therefore, the concept of utilizing anti-DFS70 antibodies as a diagnostic or prognostic discriminator of ANA-positive subjects with and without AARD is appealing, but reliable data from various clinical and diagnostic laboratory sites are mandatory to support the clinical use of this marker. Since proper reading of the DFS pattern, is crucial to ensure its usefulness in supporting clinical diagnosis, the objective of this study was to use an internet-based survey to assess how accurately the DFS IIF pattern was recognized by experienced technologists.
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