Immunoassays Correlated With Systemic Lupus Erythematosus Activity

Quantitative measurement of anti-double stranded DNA (dsDNA) antibodies plays a central role in monitoring the autoimmune connective tissue disease SLE, and results are incorporated into the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2 K).

Scientists at the University Health Network (Toronto, ON, Canada) analyzed 105 patient samples for anti-dsDNA antibodies and results were interpreted as positive or negative according to manufacturer cut-off limits. A multiplex anti-dsDNA immunoassay and an enzyme anti-dsDNA immunoassay assay were investigated as potential alternatives to the Farr-radioisotope immunoassay (RIA).

The BioPlex 2200 multiplex immunoassay (BPx, Bio-Rad Laboratories; Hercules, CA, USA) and the Quanta Lite “Farrzyme” enzyme immunoassay (EIA, INOVA Diagnostics; San Diego, CA, USA) met the stated analytical performance claims, but EIA maintained the widest measurable range. Only 33% SLE patients tested positive on BPx and only 31% with the EIA as compared with the 48% for Farr-RIA. Correlation between Farr-RIA and BPx assay results was poor with 62% positive agreement and 85% negative agreement. There was also poor correlation between the Farr-RIA and EIA with 56% lower positive agreement, but a better negative agreement of 91%.

The mean SLEDAI-2 K scores differed significantly between positive and negative result groups for Farr-RIA and BPx, but not for EIA and the authors suggest suggests it may be appropriate to lower the EIA cut-off point. The authors concluded that the optimal alternative for the Farr-RIA assay remains equivocal. There are ongoing analyses of clinical follow-up and anti-dsDNA measurements, which will aid in determining the most appropriate alternative. The article was published on August 15, 2011, in the journal Clinical Biochemistry.

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