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The P-ANCA pattern is defined as perinuclear indirect immunofluorescent (IIF) staining on ethanol fixed normal human neutrophils.1–3 This pattern is an artefact of ethanol fixation, dependent on the redistribution of certain cationic neutrophil granule proteins (such as myeloperoxidase (MPO), lactoferrin, and lysozyme) around the negatively charged nuclear membrane.1, 2 However, certain MPO-ANCA can produce cytoplasmic rather than perinuclear IIF staining,4 possibly related to a subpopulation of epitopes on MPO that do not redistribute with ethanol fixation.2 We now report that MPO-ANCA positive sera may produce a combination of P-ANCA and atypical cytoplasmic5 ANCA IIF patterns on certain ethanol fixed neutrophil substrates, potentially leading to interpretative and diagnostic difficulties.
Sera from six patients …