Low avidity antibodies to double stranded DNA in systemic lupus erythematosus: a longitudinal study of their clinical significance.

In a longitudinal study the relevance of the detection of low avidity antibodies to double stranded DNA (dsDNA) as measured by the polyethylene glycol (PEG) assay in patients with systemic lupus erythematosus (SLE) was evaluated. It was found that 35 patients positive in the PEG assay only--that is, having only low avidity anti-dsDNA in their circulation, had a mild course of their SLE with absence of renal involvement. The PEG assay had little predictive value but a high specificity (90.2%) for clinical exacerbations; furthermore, a change in avidity of anti-dsDNA in such patients was seldom observed. In 14 patients positive in both Farr and PEG assays--that is, with a relative preponderance of high avidity anti-dsDNA, there was a clear correlation between rises in Farr assay and major exacerbations, while the PEG assay on its own was not helpful in predicting disease manifestations; disease manifestations were often heralded by a change in the Farr/PEG ratio, with renal and cerebral exacerbations associated with the greatest increase in the Farr/PEG ratio (more than 10 times the previous value).