Pseudo-Elevation of Anti Double Stranded DNA IgG Antibody Caused by Rheumatoid Factor.

Background: The examination of anti-double stranded DNA (ds-DNA) IgG antibody is of great significance for the diagnosis, differential diagnosis, assessment of disease activity, and prognosis of disease recurrence in SLE.

Methods: We used a chemiluminescence method to detect ds-DNA IgG and found that the levels of ds-DNA IgG antibody in the patient's serum were significantly increased and the indirect immunofluorescence (IIF) test result was negative. Laboratory tests show that the patient's RF level far exceeds the upper limit of their reference range.

Results: RF 110.6 IU/mL, ds-DNA IgG 753 IU/mL; After PEG6000 treatment, the RF was 108.7 IU/mL, and then the ds-DNA IgG was measured at 23.5 IU/mL.

Conclusions: The RF IgM subtype is the main cause of RF interference in IgG antibody detection, mainly due to the binding of the Fc region of RF to the Fab segment of IgG. Combining with capture antibodies and labeled antibodies leads to the formation of non-specific detection signals, or directly reacting with the detected substance, resulting in false positive test results.