The clinical utility of anti-chromatin antibodies as measured by BioPlex 2200 in the diagnosis of systemic lupus erythematosus versus other rheumatic diseases

Background: The detection of autoantibodies is indispensable to systemic lupus erythematosus (SLE). Bioplex 2200 ANA screen is a multiplex immunoassay system that allows simultaneous determination of autoantibodies to extractable nuclear antigens (ENA) including anti-chromatin antibodies (ACAs). However, the clinical significance of the ACAs by this new method in SLE patients has not been studied in comparison with other rheumatic disorders. We performed a retrospective study of patients with rheumatic diseases to assess the diagnostic value of the ACAs by Bioplex 2200 method in SLE. Methods: Adult patients with rheumatic complaints seen by rheumatologists at the Cleveland Clinic between January 2008 and February 2010 were screened for positive anti-ENA antibodies by the Bioplex 2200. Patients with positive anti-ENA antibodies were classified into two populations based upon the presence and absence of the ACAs. We retrospectively studied the clinical and laboratory data of these patients. Results: A total of 764 subjects with positive anti-ENA antibodies were screened, including 115 with positive ACAs. There were 93 SLE patients consisting of 58 with positive ACAs and 35 with negative ACAs. The sensitivity, specificity, positive predictive value and negative predictive value of the ACAs in SLE were 62.4%, 91.5%, 50.4% and 94.6% respectively. Apart from SLE, positive ACAs were associated with mixed connective tissue disease (MCTD)/undifferentiated CTD (UCTD) and other autoimmune diseases. No correlation was found between the ACAs and lupus glomerulonephritis or anti-dsDNA antibodies. Conclusions: Measurement of the ACAs by the Bioplex 2200 is specific for diagnosing SLE but not useful for differentiating between SLE and MCTD/UCTD.