ANA serotypes determine diagnostic range of connective tissue diseases

Diagnosing connective tissue diseases more precisely has moved a step closer with the first study of the reactivity of antinuclear antibodies (ANAs) in a large consecutive series in a routine setting.

This, say the researchers, gives a more realistic range of diagnoses than other studies that have performed assays of reactivity in clinically diagnosed patients.

Patients positive for Sjögren’s syndrome A antibody (SSA) or SSB antibody, or both, by line immunoassay and immunodiffusion comprised 12% of the whole sample. This pattern was the commonest among 180 patients with available clinical information, indicating systemic lupus erythematosus (SLE) (45%), primary Sjögren’s syndrome (pSS) (14%), scleroderma (9%), rheumatoid arthritis (8%), cutaneous lupus (8%), and dermatomyositis (2%). Specific reactivity against Ro52, Ro60, and SSB proteins was related to particular diagnoses within the range. Reactivity to Ro52 alone pointed towards scleroderma (34%) and dermatomyositis (11%); to Ro60 SLE (80%); and to Ro60 and Ro52 SLE (52%). Results with immunodiffusion alone predicted other diagnoses within the range. The sensitivity of line immunoassay makes it the recommended method, although with triple reactivity to Ro52, Ro60, and SSB, additional immunodiffusion can discriminate between SLE and pSS.

Nearly 16 000 serum samples from over 10 500 consecutive patients during 1996–9 were tested for ANAs. Positive samples were then tested by immunodiffusion and line immunoassay versus recombinant SSA-Ro52, natural SSA-Ro60, and recombinant SSB.

Serological tests for ANAs have been augmented with recombinant Ro52 and Ro60—reactive protein determinants for SSA and SSB—although their diagnostic value was unknown until now.