Clinical Information

Measurement of antinuclear antibodies (ANA) in serum is the most commonly performed screening test for patients suspected of having a systemic autoimmune rheumatic disease (SARD), also referred to as connective tissue disease.(1) ANA occur in patients with various autoimmune diseases, both systemic and organ specific, but they are particularly common in SARDs, which  include systemic lupus erythematosus (SLE), discoid lupus erythematosus, drug-induced lupus erythematosus, mixed connective tissue disease (MCTD), Sjogren's syndrome (SjS), systemic sclerosis, CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia), and idiopathic inflammatory myopathies.

ANA can be detected by different technologies, including indirect immunofluorescence assay (IFA) and solid phase assays such as enzyme immunoassays and multiplex bead immunoassays. In a study performed in the Mayo Clinic Antibody Immunology Laboratory, no significant differences were demonstrated between ANA IFA and ANA enzyme-linked immunosorbent assay (ELISA) for a cohort of patients with connective tissue disease consisting predominantly of patients with SLE, SjS, and MCTD. Weakly positive ANA ELISA results were not a strong indicator of SARD in this laboratory cohort. The likelihood of finding an autoantibody to a specific extractable nuclear antigen including double-stranded DNA on a second-order testing increased directly with the level of ANA: 88% of sera that had detectable autoantibodies on second-order testing had an ANA level greater than 3.0 U.(2)

Overall, an ANA ELISA result of greater than or equal to 3.0 U was demonstrated as the optimal cutoff for CTDC / Connective Tissue Disease Cascade, Serum. This algorithm is intended to evaluate patients with common connective tissue diseases such as SLE, SjS, and MCTD.

For more information see Connective Tissue Disease Cascade.