Testing on formalin-fixed neutrophils is less sensitive and specific for small vessel vasculitis, and less sensitive for MPO-ANCA, than most ELISAs

Abstract

This study evaluated the usefulness of testing sera with perinuclear antineutrophil cytoplasmic antibodies (P-ANCA) on formalin-fixed neutrophils to differentiate between vasculitis and other diseases, and to distinguish between myeloperoxidase (MPO) and other antigen targets. Sera from active (n=24) or treated vasculitis (n=23) and non-vasculitic disease (n=37) were tested in 3 ethanol- and 2 formalin-fixed neutrophil assays, and in 12 MPO-ANCA ELISAs. The sensitivity of demonstrating that P-ANCA became cytoplasmic on formalin-fixed cells in vasculitis, and negative in non-vasculitic disease was 75-79% in different assays compared with 88% for positivity in the majority of MPO-ANCA ELISAs. ..