CytoBead ANA 2 assay - a novel method for the detection of antinuclear antibodies
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Background : Detection of anti-nuclear autoantibodies (ANA) is based on a two-step algorithm including indirect immunofluorescence (IIF) on HEp2 cells and subsequent reflex/confirmatory testing for specific autoantibodies. Simultaneous cell- and microbead-based autoantibody detection by IIF may be utilized for the evaluation of systemic autoimmune rheumatic diseases (SARDs). In the present study, we assessed the performance of CytoBead ANA 2 in the detection of ANA and ANA-specific autoantibodies, compared to ANA IIF and BioPlex™ 2200. We also tested the ability of CytoBead ANA DFS-70 to identify dense-fine speckled (DFS) pattern associated with anti-DFS70 antibodies in non-SARDs patients. Methods : Hundred-twelve routine sera samples were assessed by manual CytoBead ANA 2 for the presence of ANA and specific autoantibodies. In parallel, these samples were analyzed by HEp2 ANA IIF test and a subsequent multiplexed assay BioPlex™ 2200 ANA. Twenty-nine ANA-positive samples obtained from non-SARDs patients and exhibiting DFS pattern by ANA IIF were further tested by CytoBead ANA DFS-70. Results: A substantial agreement was observed between classical ANA IIF and manual CytoBead ANA 2 for the detection of ANA (k = 0.74). Discordant results were mainly associated with the presence of anti-SSA/Ro antibodies detected by CytoBead ANA 2 in ANA IIF negative patients. A good to almost perfect agreement was found between CytoBead ANA 2 and BioPlex™ 2200 for detection of specific antibodies with kappa values ranging from 0.70 - 0.90. Twenty samples (68.9 %) obtained from 29 ANA IIF positive without SARDs patients exhibited DFS pattern in CytoBead ANA DFS-70, which confirmed the presence of anti-DFS70 antibodies. Conclusion: The diagnostic performance of manual CytoBead ANA 2 for ANA screening and detection of ANA specific antibodies is comparable to the diagnostic performance of ANA IIF followed by BioPlex™ 2200. This novel one-step assay enables simultaneous ANA screening and confirmation and represents a promising alternative approach to the time-consuming and costly two-tier ANA analysis.
