Diagnostic performance of assays for urgent MPO, PR3 and GBM autoantibodies in suspected vasculitis

Rapid testing for antineutrophil cytoplasmic antibodies (ANCAs) and glomerular basement membrane (GBM) antibodies may assist in the early diagnosis of small vessel vasculitis. Clinical utility of urgent testing of these antibodies in an Australian context is not known. Our retrospective study examined the urgent test requests for ANCA and/or GBM antibodies performed over a 2-year period. Overall, urgent testing was positive in 28.6% of all requests. When cases of known ANCA-associated vasculitis or GBM disease were excluded, the urgent test positive rate remained high at 23%. The highest rates of new positivity were seen in patients with acute renal impairment and haemoptysis (71%), isolated acute renal impairment (21%) and isolated haemoptysis (18%). Dual positivity with both ANCAs and anti-GBM antibodies occurred in four patients. Our study confirms that clinicians requesting urgent testing are able to identify patients with a high pretest probability for small vessel vasculitis, thus allowing for rapid serological diagnosis.