Algorithm for antinuclear antibodies in subjects with clinical suspicion of autoimmune diseases.

Objectives: Antinuclear antibodies (ANA) are fundamental in the diagnosis of systemic autoimmune rheumatic diseases (SARDs). Different assays for ANA screening are available, such as indirect immunofluorescence (IIF) on HEp-2 cells and Multiplex fluorescent immunoassay (MFI). This study aimed to clarify the importance of ANA detected only by IIF in the future development of SARDs and to recommend a laboratory algorithm that integrates the available diagnostic approaches to optimise the diagnosis of ANA IIF+MFI- subjects.
Methods: A total of 9,291 subjects with clinical suspicion of SARDs were evaluated for ANA by IIF and MFI. One hundred and ninety-eight subjects (2.1%) were ANA IIF+MFI-, who were followed up for 2 years. ANA were evaluated using IIF on HEp-2 cells and MFI on the BioPlex 2200.
Results: The ANA IIF+MFI- cohort included 106 subjects with SARDs, 26 subject with other autoimmune diseases (not-SARDs) and 66 subjects with minor symptoms or ANA requested in check-ups. Only 94 subjects underwent re-evaluation. After a 2-year follow-up, most re-evaluated subjects (51 patients) became ANA negative for both assays (mainly rheumatoid arthritis, polymyalgia and inflammatory bowel disease patients) and 35 subjects remained ANA IIF+MFI- (principally systemic sclerosis and systemic lupus erythematosus patients). A new algorithm for ANA evaluation was suggested.
Conclusions: According to the proposed algorithm, ANA IIF+MFI- subjects should be screened by an alternative solid-phase assay such as line-immunoassay or ELISA.