P35 Measuring dsDNA antibodies in the elderly: positive results rarely indicate lupus

Background Antibodies to dsDNA are reported to be specific for lupus and are included in the main classification criteria, although pitfalls when used as a ‘screening’ test in patients with multiple medical symptoms have been described. Lupus is typically diagnosed in the first 50 years of life and clinically active disease is unusual in the elderly. We evaluated dsDNA requests made in elderly patients (>80 years) in our centre. Methods Review of 23,287 consecutive dsDNA antibody requests made through the University of Birmingham Immunology Lab between 2009 and 2019. Review of available clinical records for patients with positive results. Results 993 dsDNA antibody requests were made for patients >80 years old (mean 84.2 years), representing 0.04% of total requests. 578 were female, 411 were male and 5 unknown. 138 (13.9%) requests were made from primary care, 80 (8.0%) from the critical care/emergency department, 623 (62.5%) from medical wards and outpatients and 97 (4.4%) from rheumatology. The remainder were from neighbouring hospitals. 67 patients (6.7%) tested positive for dsDNA by ELISA (lab normal range) and 31 (3.1%) by Crithidia. Clinical records were available for 58 patients with positive dsDNA antibodies. Three were known to have longstanding SLE. No patients were diagnosed as having SLE at or after the time of dsDNA antibody testing. Sixteen patients had other autoimmune diseases including rheumatoid arthritis, Sjogrens Syndrome, myasthenia gravis, microscopic polyangiitis, polymyalgia rheumatica, bullous pemphigoid and immune thrombocytopenia. Four patients had underlying malignancy (one each of lung, prostate, bladder and colon). The remainder had a mix of infections and general medical presentations. One hundred randomly selected patients with negative dsDNA antibody were reviewed and no cases of lupus were identified, leading to a calculated specificity of dsDNA antibodies for lupus of only 64.5%. Conclusions Antibodies to dsDNA are not uncommon in unwell elderly patients presenting to hospital or primary care. They are rarely indicative of SLE. The reported high specificity of dsDNA antibodies for lupus are not applicable in this age group.