Effects of rheumatoid factor, antinuclear antibodies and plasma reagin on the serologic assay for Lyme disease.

Rheumatoid factor (RF), antinuclear antibodies (ANA) and the presence of other spirochetal infections have been reported to be the source of false positive serologic tests of Lyme disease. To evaluate this, we studied their effect upon the Lyme assay in use in our clinical laboratory. Of 64 rapid plasma reagin (RPR) test positive sera, 2 had positive Lyme antibody tests, not statistically different than controls. Of 43 RF positive sera, 2 had positive lyme tests, no different than controls, and 1 of 53 ANA containing sera had positive Lyme tests, again, not different from controls. There was no relationship of titer of RPR or ANA with Lyme results, nor of ANA pattern. Sera containing high titer RF, however, had slight interference, producing an increase in equivocal Lyme assay results. From the other point of view, sera that were Lyme test positive had no increased frequency of RPR or RF, but had an increased frequency of ANA. Therefore, neither RPR, RF or ANA were found to markedly interfere with the Lyme assay. However, Lyme antibodies may interfere with the ANA test.