The aims of this study were to establish the frequency, demographic and clinical characteristics of Ha, Ks, and Zo antibody-positive patients in a referral setting, and to evaluate the performance of a line immunoblot assay (LIA) for detection of Ha, Ks, and Zo antibodies.

Consecutive samples received at ARUP Laboratories for myositis antibody testing were screened by protein immunoprecipitation (IP) of S³⁵-labeled K562 cells. Antinuclear antibodies (ANA) were detected by indirect immunofluorescence. Samples with distinct bands corresponding to approximately 59, 65, or 60 and 70 kDa were identified as suspicious of Ha, Ks and Zo, respectively, and tested for these antibodies by LIA. As controls, samples positive for other autoantibodies associated with myositis or other autoimmune diseases and self-proclaimed healthy donors were also evaluated by LIA. Clinical and laboratory data for all Ha, Ks, and Zo antibody-positive patients were sought to confirm diagnosis.

We report on the frequency of detection of Ha, Ks and Zo antibodies in a reference laboratory setting and agreement between LIA and IP for detection of these antibodies. We also describe the clinical characteristics of patients found positive for antibodies against Ha, Ks, and Zo. 

Identification of Ha, Ks, and Zo antibodies is important for diagnosis, prognosis, and disease management in patients with ASyS. LIA confirmed the presence of Ha, Ks, or Zo antibodies in patients with corresponding bands observed in the IP assay. Combined use of both methods improves reliability for the diagnosis of ASyS in patients undergoing evaluation for inflammatory myopathies.