MPO - Myeloperoxidase ( Myeloid Cell Marker)

MPO positive in myeloid cells means they contain the enzyme myeloperoxidase, found in azurophilic granules of neutrophils and monocytes. MPO generates reactive oxidants (e.g., hypochlorous acid) for microbial killing. Cytochemical or immunophenotypic MPO positivity is used diagnostically to confirm myeloid lineage (versus lymphoid) in blood or bone marrow and helps classify leukemias.

Myeloperoxidase (MPO) is an enzyme released by activated neutrophils and monocytes and serves as a marker of neutrophil activation, oxidative stress and systemic inflammation. Elevated MPO levels indicate heightened inflammatory activity and are linked to endothelial dysfunction, atherosclerotic plaque instability and increased risk of acute coronary syndromes, heart attack and other inflammatory conditions.

MPO positive means cells contain the enzyme myeloperoxidase, identified by staining or flow cytometry. It reflects myeloid-lineage cells (neutrophils, monocytes) or neutrophil activation. Clinically, MPO positivity supports a diagnosis of myeloid neoplasms such as acute myeloid leukemia and helps distinguish myeloid from lymphoid malignancies; it can also indicate active inflammation or infection.

Acute monocytic leukemia (FAB M5) is typically myeloperoxidase (MPO)–negative or only weakly positive because the malignant cells are monocytic. Diagnosis depends more on nonspecific esterase staining and monocytic markers (CD14, CD64, CD11c). A minority of cases may show focal or weak MPO reactivity, so MPO positivity is uncommon but possible.

No — MPO is an enzyme inside neutrophils, while ANCA are autoantibodies directed against neutrophil cytoplasmic proteins. One ANCA subtype specifically targets MPO (called MPO‑ANCA or p‑ANCA). MPO itself is not an ANCA, but can be the antigen for MPO‑ANCA. Testing distinguishes the antigen and antibody for diagnosis and management.

To test for myeloperoxidase (MPO) in leukemia, labs perform MPO cytochemical staining on peripheral blood or bone marrow smears and use intracellular anti‑MPO flow cytometry. Immunohistochemistry on marrow or biopsy specimens is an alternative. MPO positivity indicates myeloid differentiation (supporting acute myeloid leukemia) and is interpreted alongside morphology, other immunophenotypic markers, and cytogenetic/molecular results.