Overview
Myeloperoxidase is a heme-containing enzyme predominantly found in the azurophilic granules of neutrophils, with smaller amounts present in monocytes and certain macrophage subpopulations. It plays a critical role in innate immunity by contributing to the oxidative burst used to kill invading microorganisms. Myeloperoxidase generates reactive oxidants such as hypochlorous acid, which are highly effective in microbial killing. Beyond host defense, MPO has been increasingly implicated in inflammatory processes, cardiovascular disease, neurodegenerative disorders, renal disease, and cancer. Its ability to create a hypermutagenic and pro-inflammatory environment links MPO to tumor initiation, progression, cell migration, apoptosis, and metastasis.
Symptoms
Abnormal myeloperoxidase levels do not cause specific symptoms on their own. Clinical manifestations depend on the underlying condition associated with altered MPO activity. Elevated MPO levels are often seen in inflammatory and infectious states, cardiovascular disorders, autoimmune diseases, vasculitides, and malignancies. Patients may present with symptoms such as fever, fatigue, chest pain, joint pain, neurological complaints, or features related to leukemia and lymphoma. MPO deficiency, although uncommon, may increase susceptibility to certain infections due to impaired microbial killing.
Causes
Increased myeloperoxidase levels arise from enhanced activation and degranulation of neutrophils during inflammation, infection, or tissue injury. Cardiovascular conditions such as coronary artery disease, unstable angina, and acute myocardial infarction are commonly associated with elevated MPO. Autoimmune and inflammatory diseases, including systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis, also show increased MPO activity. Elevated levels are observed in hematological malignancies such as acute myeloid leukemia, lymphomas, and in solid tumors, where MPO contributes to oxidative stress and tumor progression. Smoking is a recognized factor associated with higher MPO levels.
Risk Factors
Risk factors for abnormal MPO levels include chronic inflammation, autoimmune disorders, cardiovascular disease, malignancy, smoking, and systemic infections. In hematological disorders, MPO expression is particularly important for identifying myeloid lineage, especially in acute myeloid leukemia and myeloid sarcoma. Technical factors such as improper sample handling, delayed serum separation, or interpretative limitations of staining methods may influence results. Because MPO lacks absolute specificity, reliance on MPO alone without clinical correlation and additional markers can lead to diagnostic uncertainty.
Prevention
There are no specific measures to prevent changes in myeloperoxidase levels, as they reflect underlying pathological processes. Prevention focuses on early detection, appropriate testing, and management of associated conditions. Proper blood and tissue sample collection, timely processing, and correct storage are essential for reliable results. In patients with elevated MPO linked to cardiovascular risk, lifestyle modifications such as smoking cessation, heart-healthy diet, weight control, blood pressure management, and lipid reduction are recommended. Accurate interpretation of MPO levels, combined with clinical findings and complementary investigations, supports early diagnosis, prognostic assessment, and effective management of inflammatory, cardiovascular, and malignant diseases.
