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Anti-chromatin antibodies, measured by ELISA, can be detected in 69% of patients with systemic lupus erythematosus (SLE) but only 7–10% of those with primary Sjogren’s syndrome, systemic sclerosis, and primary antiphospholipid syndrome (APS). The antibody was not present in 100 healthy blood donors, acting as controls.
Of the patients with SLE, 52 of 100 had evidence of lupus nephropathy and 42 of these were positive for anti-chromatin antibody, yielding a sensitivity of these antibodies for lupus nephritis of 81% and a specificity of 39%. The mean level was 68U in those with nephropathy and 42U in those without. There was a significant correlation between disease activity and antibody level (R2=0.0689).
Anti-chromatin antibodies did not correlate with the presence of ANA, antiphospholipid antibodies or rheumatoid factor. Using the Farr assay, six samples were anti-dsDNA positive but anti-chromatin antibody negative, possibly because some antibodies recognise structures of DNA that can occur in protein-free DNA in solution but not when DNA is wrapped around the histones in chromatin bound to the solid phase of the ELISA plate.
Measuring anti-chromatin antibodies is a useful addition to the laboratory tests that can help in diagnosis of SLE and can be a useful marker for an increased risk of nephropathy.