MPOpositive

MPO-positive is a medical descriptor used to indicate the presence of myeloperoxidase (MPO) in cells or in blood. Myeloperoxidase is an enzyme found in azurophilic granules of neutrophils and, to a lesser extent, monocytes. The term is commonly encountered in hematology, pathology, and autoimmunity contexts.

Detection methods: MPO positivity can be demonstrated by cytochemical staining of smears (historically benzidine-based MPO staining) or by immunohistochemistry on tissue sections, and by flow cytometry or enzyme assays on cells. In diagnostic pathology, MPO positivity of blast cells supports a myeloid lineage and helps distinguish acute myeloid leukemia from lymphoblastic leukemias; Auer rods, when present, are highly suggestive of MPO positivity.

MPO-ANCA positivity refers to circulating antibodies directed against MPO and is clinically relevant in certain vasculitides, notably microscopic polyangiitis and, less frequently, granulomatosis with polyangiitis. Serological MPO positivity is used in combination with clinical criteria and imaging to establish diagnosis and monitor disease.

Interpretation and limitations: The significance of MPO positivity depends on context: tissue staining in hematology indicates lineage or differentiation; serum MPO-ANCA positivity signals an autoimmune process. False positives can occur due to non-specific staining or technical issues, and results should be interpreted alongside other laboratory and clinical findings.

See also: myeloperoxidase; MPO-positive staining; anti-myeloperoxidase antibodies; ANCA.