ANCA in haemodialysis patients

The prevalence of positive ANCA as well as the prevalence ofPR-3 and MPO antibodies were examined in a cross-sectional sampleof 1277 haemodialysis patients from 16 German haemodialysiscentres. We found 32 patients positive for c-ANCA (median titre1:40; range 1:20–1:320) and 65 for p-ANCA (1:80; 1:20–1:1280).Twenty-two percent of the c-ANCA-positive and 31% of the p-ANCA-positivepatients had PR-3 and MPO antibodies by ELISA respectively.Clinical evidence of vasculitis was found in 11 of 32 c-ANCA-positiveand 19 of 65 p-ANCA-positive patients. Of the 11 c-ANCA-positive,four had a known diagnosis of Wegener's granulo-matosis (WG);WG was recognized after the test in a further five patientsand two had renal limited RPGN. Of the 19 p-ANCA-positive patients,three had a clinical diagnosis of microscopic polyarteritis(MP), MP was newly diagnosed in a further 12, WG in one andrenal limited RPGN in three. The patients had not received cyclophosphamide(the diagnosis had been non-specified ‘systemic disease’).Thus false-positive ANCA, as defined by absence of vasculitis,was found in 5% of dialysis patients versus 0% in patients withpreterminal renal failure {n=152) or blood donors (n=150). Patientswith vasculitis tended to have higher c-ANCA and p-ANCA titresrespectively, but there was a considerable overlap. Titres werenot higher in patients symptomatic at the time of examination(6 of 11 c-ANCA and 10 of 19 p-ANCA), but PR-3 and MPO ELISAwere positive in all but two. Thus c-ANCA were false positive(i.e. not associated with clinical vasculitis) in 66% and p-ANCAin 71%. In some patients ANCA was positive, but ELISA negative. We conclude that (i) in dialysis patients c-ANCA and p-ANCAare frequently present in the absence of vasculitis; (ii) specificitycan be improved, but sensitivity is lost, by using PR-3 andMPO ELISA respectively; (iii) serology permits the recognitionof WG or MP in cases where the diagnosis has been missed. Itis recommended that all patients with unknown primary renaldisease admitted to renal replacement therapy be examined usingboth ANCA-IF and PR-3/MPO ELISA.