Myeloperoxidase, usually shortened to MPO, is an enzyme released mainly by activated white blood cells called neutrophils and monocytes. In the right place, MPO helps the immune system kill microbes. In the wrong place, especially inside artery walls, MPO can fuel oxidative stress, irritate the blood vessel lining, modify cholesterol particles, and contribute to unstable plaque. That is why the MPO blood test is used as a cardiovascular inflammation marker rather than a standard cholesterol marker.
A high MPO result does not diagnose a heart attack, blocked artery, or specific disease by itself. It suggests that inflammatory white-cell activity and oxidative stress may be higher than expected, which can add risk beyond LDL cholesterol, blood pressure, diabetes, smoking, and family history. The result is most useful when it is interpreted with a full cardiovascular risk picture, including symptoms, medical history, lipid markers, glucose control, kidney function, and other inflammation tests.
- An MPO test measures free myeloperoxidase in blood, usually reported in pmol/L.
- Common MPO risk cutoffs are low risk under 470 pmol/L, moderate risk 470–539 pmol/L, and high risk at 540 pmol/L or higher.
- High MPO often points to active inflammation and oxidative stress, but it can rise from cardiovascular disease, infection, smoking, strenuous exercise, autoimmune disease, kidney disease, and other inflammatory conditions.
- MPO is not a heart attack rule-out test; chest pain, shortness of breath, sweating, fainting, or pain spreading to the arm, jaw, back, or neck needs urgent medical care.
- Fasting is usually not required for MPO alone, but fasting may be requested when it is ordered with a lipid panel, glucose, insulin, or other cardiometabolic tests.
Table of Contents
- What the MPO Test Measures
- Normal Range and High MPO Results
- Why High MPO Relates to Artery Inflammation
- Causes of High MPO
- MPO and Other Heart Risk Markers
- Who May Benefit From MPO Testing
- What to Do After a High MPO Result
- Low MPO, Repeat Testing, and Limitations
What the MPO Test Measures
The MPO test measures myeloperoxidase circulating outside white blood cells in the bloodstream. MPO is stored inside neutrophils and monocytes, two types of immune cells that respond quickly to infection, tissue injury, and inflammation. When these cells become activated, they can release MPO into surrounding tissues and blood.
MPO’s normal immune role is protective. It helps white blood cells produce strong oxidants, including hypochlorous acid, to kill bacteria and other pathogens. The problem begins when too much MPO activity occurs around blood vessels or inside atherosclerotic plaque. In that setting, the same chemistry that helps kill microbes can damage nearby proteins, lipids, and vessel-wall tissue.
The test is usually ordered as part of an advanced cardiovascular risk assessment. It is not part of a standard lipid panel, and it is not the same as LDL cholesterol, HDL cholesterol, triglycerides, ApoB, Lp(a), hs-CRP, or troponin. MPO gives a different kind of information: it reflects activated inflammatory white-cell activity and oxidative stress.
Most commercial MPO cardiovascular tests report results in pmol/L. The blood draw feels like a routine venipuncture. The lab, however, must handle the specimen correctly because MPO can be affected by sample processing. Some labs specify plasma rather than serum, refrigerated transport, prompt separation from blood cells, and avoidance of certain collection tubes. For patients, the most important point is simple: use the lab’s own instructions and interpret the result using that lab’s reference ranges.
MPO is sometimes described as a “vascular inflammation” marker. That phrase is helpful, but it can be too narrow. MPO can rise from artery inflammation, but it can also rise from non-cardiovascular inflammation. A high result should start a careful search for likely causes rather than an automatic assumption that the arteries are the only source.
Normal Range and High MPO Results
MPO reference ranges vary by laboratory and test method, but many cardiovascular risk reports use three broad categories: low, moderate, and high. These ranges are risk categories, not disease diagnoses.
| MPO result | Common interpretation | What it may suggest |
|---|---|---|
| Under 470 pmol/L | Low risk category | No major MPO signal on that test, though other risk factors can still be present |
| 470–539 pmol/L | Moderate risk category | Possible increased inflammatory or oxidative activity; repeat testing and risk review may be useful |
| 540 pmol/L or higher | High risk category | Higher white-cell oxidative activity and possible residual cardiovascular inflammatory risk |
A high MPO result means the value is above the lab’s cardiovascular risk cutoff, often 540 pmol/L or higher. It does not tell you where the inflammation is located. It also does not show whether a plaque is present, how narrowed an artery is, or whether a plaque is about to rupture.
A moderate MPO result deserves context. For example, 500 pmol/L in a person who smoked before the test, had gum inflammation, and completed a very hard workout the day before may mean something different from 500 pmol/L in a person with known coronary artery disease, diabetes, and recurrent chest symptoms. Trends can also matter. A single borderline result may be less useful than repeated high results that persist after obvious temporary triggers have resolved.
A low MPO result is generally reassuring for this specific marker, but it does not cancel other risks. A person can have low MPO and still have high LDL-C, high ApoB, high Lp(a), high blood pressure, diabetes, chronic kidney disease, or a strong family history of early heart disease. MPO should never be used as a “permission slip” to ignore major risk factors.
Some reports may include the assay’s analytical range, such as the lowest and highest values the test can reliably report. That is different from the clinical risk range. For example, a test may be technically able to measure a wide span of MPO values, but the clinical report may still group results into low, moderate, and high risk categories.
Why High MPO Relates to Artery Inflammation
High MPO is linked to cardiovascular risk because MPO participates in several processes that can make artery plaque more inflammatory, more oxidized, and less stable. The connection is biological, not just statistical.
Atherosclerosis begins when cholesterol-rich particles enter the artery wall and trigger an immune response. Over time, immune cells, cholesterol, scar-like tissue, calcium, and cellular debris can form plaque. Some plaques grow slowly and become stable. Others develop a thin cap, a large inflammatory core, or surface erosion that makes them more likely to trigger a clot.
MPO can contribute to this risky environment in several ways.
First, MPO promotes oxidative stress. Oxidative stress means reactive molecules are being produced faster than the body can neutralize them. In the artery wall, this can damage proteins, lipids, and the vessel lining.
Second, MPO can modify LDL particles. Oxidized or otherwise modified LDL is more likely to be taken up by immune cells in the artery wall, helping create foam cells and plaque inflammation. This is one reason MPO is closely related to the topic of oxidized LDL.
Third, MPO can impair HDL function. HDL cholesterol is often called “good cholesterol,” but the HDL number on a lab report does not fully describe how well HDL works. MPO can modify ApoA1 and HDL particles, reducing their ability to help remove cholesterol from artery-wall cells and calm inflammation. This is one reason very high or normal HDL-C does not always guarantee low risk.
Fourth, MPO can reduce nitric oxide availability. Nitric oxide helps blood vessels relax, supports healthy blood flow, and protects the vessel lining. When nitric oxide activity falls, arteries may become stiffer, more reactive, and more prone to endothelial dysfunction.
Fifth, MPO may contribute to plaque instability. When inflammatory cells release MPO inside or around plaque, the local chemistry can weaken protective structures, increase tissue injury, and make the plaque surface more vulnerable. A vulnerable plaque may not cause severe narrowing before it causes a heart attack or stroke. This is one reason inflammation markers can add information that cholesterol numbers alone may miss.
MPO is best understood as a marker of active inflammatory biology. It does not replace imaging, cholesterol testing, blood pressure measurement, diabetes screening, or symptom evaluation. It adds another layer: whether a white-cell-driven oxidative process appears elevated at the time of testing.
Causes of High MPO
High MPO can come from cardiovascular and non-cardiovascular sources. The result should be interpreted alongside recent illness, medications, exercise, smoking, dental health, autoimmune disease, kidney function, and liver health.
| Possible cause | Why it can raise MPO | What to review |
|---|---|---|
| Atherosclerosis or coronary artery disease | Inflamed plaque can attract activated white blood cells | Lipid markers, symptoms, blood pressure, diabetes status, imaging history |
| Smoking or vaping nicotine products | Tobacco-related oxidative stress activates inflammatory pathways | Current use, secondhand smoke, quit plan |
| Insulin resistance or type 2 diabetes | High glucose and metabolic inflammation increase vascular stress | Fasting glucose, HbA1c, fasting insulin, waist size, triglycerides |
| Periodontal disease | Chronic gum inflammation can activate neutrophils | Bleeding gums, dental infections, recent dental care |
| Recent infection or inflammatory illness | White blood cells release MPO during immune activation | Fever, respiratory symptoms, urinary symptoms, recent antibiotics |
| Autoimmune or inflammatory disease | Conditions such as rheumatoid arthritis, lupus, and vasculitis can activate immune cells | Joint swelling, rashes, autoimmune history, ESR or CRP results |
| Chronic kidney disease | Kidney disease is linked with inflammation, oxidative stress, and higher cardiovascular risk | Creatinine, eGFR, urine albumin, blood pressure |
| Very strenuous exercise before testing | Intense exertion can temporarily increase inflammatory and oxidative markers | Heavy training, races, long endurance sessions, muscle injury |
The pattern matters more than the number alone. A high MPO in a person with recent flu-like symptoms may need repeat testing after recovery. A high MPO in a smoker with high ApoB, high triglycerides, high blood pressure, and a family history of early heart disease points toward a broader cardiometabolic risk problem.
Periodontal disease is easy to overlook. Inflamed gums can produce a chronic immune signal, and many people do not connect bleeding gums with blood vessel risk. If MPO is high and the cause is not obvious, dental inflammation deserves attention.
Insulin resistance is another common contributor. High triglycerides, low HDL-C, increased waist circumference, high fasting insulin, fatty liver, prediabetes, and type 2 diabetes often cluster with vascular inflammation. If glucose metabolism is part of the concern, tests such as HbA1c, fasting glucose, fasting insulin, and sometimes HOMA-IR can help clarify the pattern.
A high MPO result should also be interpreted cautiously during acute illness. Testing during infection, injury, flare-ups of inflammatory disease, or the days after intense exercise can make the result harder to interpret. In many non-urgent cases, repeating MPO after the temporary trigger has passed gives a cleaner signal.
MPO and Other Heart Risk Markers
MPO works best as part of a wider cardiovascular risk assessment. It answers a different question from cholesterol and glucose tests, so it should be combined with them rather than substituted for them.
LDL-C estimates the amount of cholesterol carried in LDL particles. ApoB estimates the number of atherogenic particles, including LDL, VLDL remnants, IDL, and Lp(a). For many people, ApoB testing gives a clearer sense of particle-related plaque risk than LDL-C alone. MPO adds information about inflammatory and oxidative activity, not particle number.
Lp(a) is mostly genetic and can increase lifetime risk for atherosclerosis and calcific aortic valve disease. A person with high Lp(a) and high MPO may have both a particle-driven inherited risk and an inflammatory risk signal. Lowering LDL-C and ApoB aggressively often becomes more important when Lp(a) is high, even though standard lifestyle changes usually have little effect on Lp(a) itself.
hs-CRP is a general inflammation marker produced mainly in response to liver signaling. It can rise from infection, obesity, autoimmune disease, trauma, and chronic inflammatory states. MPO is more closely tied to activated neutrophils and oxidative enzyme activity. A high hs-CRP test and high MPO together may suggest a stronger inflammatory pattern than either marker alone, but the source still needs clinical evaluation.
Lp-PLA2 is another vascular inflammation marker. It is associated with lipoprotein-associated inflammatory activity and plaque biology. MPO and Lp-PLA2 testing can overlap in cardiovascular risk assessment, but they do not measure the same process.
Troponin is completely different. Troponin rises when heart muscle cells are injured, such as during a heart attack or other forms of cardiac injury. MPO may be studied in acute coronary settings, but it does not replace emergency evaluation or high-sensitivity troponin testing for chest pain.
A practical way to think about these markers is:
- LDL-C, non-HDL-C, ApoB, LDL-P, and Lp(a) describe cholesterol particle burden.
- hs-CRP, MPO, and Lp-PLA2 describe inflammatory or vascular injury pathways.
- HbA1c, fasting glucose, fasting insulin, and triglyceride patterns describe metabolic risk.
- Blood pressure, kidney function, smoking, age, sex, family history, and imaging results shape the overall risk estimate.
- Troponin and BNP belong more to acute injury or heart strain evaluation than routine plaque-risk screening.
No single blood marker can fully predict heart attack or stroke. Cardiovascular events usually arise from several overlapping problems: particle burden, blood pressure stress, clotting tendency, inflammation, endothelial dysfunction, metabolic disease, smoking, genetics, kidney disease, and plaque structure. MPO is one piece of that larger picture.
Who May Benefit From MPO Testing
MPO testing may be most useful for people who already have reasons to look beyond a basic cholesterol panel. It is often considered when standard risk markers do not fully explain the concern, or when a clinician is trying to identify residual inflammatory risk.
A clinician may consider MPO testing in someone with:
- Known coronary artery disease, stroke, peripheral artery disease, or carotid plaque
- Multiple risk factors, such as high blood pressure, diabetes, smoking, obesity, chronic kidney disease, or strong family history
- Intermediate cardiovascular risk where additional risk information may change treatment intensity
- High LDL-C, high ApoB, high Lp(a), high triglycerides, or metabolic syndrome
- Persistent inflammation markers without a clear explanation
- Concern for residual risk despite treatment with statins or other preventive therapy
MPO testing may be less useful when the result will not change management. For example, a person with very high established risk may already need intensive treatment regardless of MPO. At the other end, a young healthy person with no symptoms, excellent metabolic markers, no family history, and no risk factors may receive little practical benefit from a single MPO value.
MPO is also not a screening test for every inflammatory disease. It may rise in inflammatory conditions, but it does not tell you whether the cause is infection, autoimmune disease, cancer, gum disease, kidney disease, or artery inflammation. When symptoms point away from the heart, the evaluation should follow those symptoms.
People with chest pain should not use MPO to decide whether to seek care. Sudden chest pressure, shortness of breath, fainting, new severe weakness, sudden sweating, pain radiating to the arm or jaw, or stroke-like symptoms need urgent evaluation. In that setting, emergency clinicians rely on symptoms, ECG findings, troponin testing, vital signs, imaging when needed, and repeated assessments. MPO is not fast or specific enough for home triage.
For preventive care, the best use of MPO is as a risk refinement tool. It can help identify a person whose inflammatory and oxidative risk seems higher than expected, prompting a more serious look at risk-factor control, lifestyle exposures, dental disease, metabolic health, and medication adherence.
What to Do After a High MPO Result
A high MPO result should lead to a structured review, not panic. The right response depends on symptoms, overall risk level, and whether there are temporary reasons for inflammation.
Start by checking whether the test was done during a noisy period. Recent infection, fever, injury, surgery, dental infection, autoimmune flare, heavy endurance exercise, or intense strength training can raise inflammatory markers. If one of these was present, a repeat test after recovery may be more informative.
Next, review the major cardiovascular risk drivers. MPO may be high because the artery environment is inflamed, but the most proven ways to reduce cardiovascular events still focus on treating established risks. That includes lowering LDL-C and ApoB when elevated, controlling blood pressure, treating diabetes or insulin resistance, stopping smoking, improving sleep, increasing physical activity, and addressing obesity when present.
A high MPO result often justifies a closer look at lipid particle burden. LDL-C can look acceptable while ApoB, non-HDL-C, remnant cholesterol, or LDL particle number remains high. An advanced lipid panel may help when the standard lipid panel does not match the person’s risk.
Metabolic health also deserves attention. High triglycerides, low HDL-C, fatty liver, prediabetes, type 2 diabetes, and central weight gain can all travel with inflammation. A metabolic syndrome blood test panel can help organize that pattern by looking at glucose, insulin, cholesterol, triglycerides, and related risk markers.
Dental care can be surprisingly important. If gums bleed during brushing or flossing, if there is chronic bad breath, loose teeth, dental pain, or known periodontal disease, treatment may reduce a chronic inflammatory burden. Dental inflammation should not be treated as separate from vascular health.
Lifestyle steps that may help lower inflammatory and oxidative stress include:
- Stop smoking and avoid secondhand smoke.
- Follow a Mediterranean-style or minimally processed diet pattern rich in vegetables, legumes, fruit, whole grains, fish, nuts, olive oil, and high-fiber foods.
- Replace trans fats and excess saturated fats with unsaturated fats when appropriate.
- Build regular aerobic activity and resistance training, but avoid testing right after unusually hard exercise.
- Treat sleep apnea if symptoms include loud snoring, choking at night, morning headaches, or daytime sleepiness.
- Manage blood pressure consistently, not only during office visits.
- Treat autoimmune or inflammatory disease flares with appropriate medical care.
- Keep vaccinations and infection prevention up to date when relevant to personal risk.
Medication decisions should be individualized. A high MPO value alone does not automatically mean someone needs a statin, aspirin, anti-inflammatory drug, or imaging test. But when MPO is high along with high ApoB, known plaque, diabetes, smoking, kidney disease, or strong family history, clinicians may reasonably consider more intensive prevention.
Aspirin deserves special caution. It can reduce clotting risk in some higher-risk people, but it can also cause serious bleeding. It should not be started only because MPO is high unless a clinician has weighed the person’s cardiovascular and bleeding risks.
Low MPO, Repeat Testing, and Limitations
Low MPO usually means the test did not detect an elevated MPO-related inflammatory signal at that time. In cardiovascular risk assessment, that is generally favorable. It does not mean the immune system is weak, and it does not rule out atherosclerosis.
Very low MPO due to inherited MPO deficiency is a different issue from a low cardiovascular MPO test result. True MPO deficiency is uncommon and is usually identified through blood cell or immune-related testing, not through routine heart-risk screening. Most people with a low MPO cardiovascular result simply fall into the low-risk category for that marker.
Repeat testing may be useful when the first result is high or moderate and the context is unclear. A common practical approach is to repeat the test after temporary inflammatory triggers have resolved. The timing depends on the situation, but waiting several weeks after an infection, dental procedure, acute injury, or unusually intense exercise often gives a cleaner result. A clinician may also repeat MPO after treatment changes, such as smoking cessation, improved periodontal care, better glucose control, or lipid-lowering therapy.
MPO has several limitations:
- It is not specific to the heart or arteries.
- It does not diagnose coronary artery disease.
- It does not measure plaque size or artery narrowing.
- It does not replace LDL-C, ApoB, Lp(a), blood pressure, diabetes testing, kidney function, or clinical judgment.
- It can be affected by sample handling and lab method.
- It may be less helpful when the result will not change treatment decisions.
The strongest use of MPO is in context. A high result can sharpen attention on residual inflammatory risk, especially when other risk factors are already present. A low result can be reassuring, but only for the MPO pathway. The most reliable cardiovascular prevention plan still comes from combining symptoms, family history, physical exam, blood pressure, cholesterol and particle markers, glucose metabolism, kidney function, lifestyle risks, and imaging when appropriate.
References
- Cardio IQ Myeloperoxidase (MPO) | Test Summary | Quest Diagnostics 2026 (Test Directory)
- Association of MPO levels with cardiometabolic disease stratified by atherosclerotic cardiovascular risk and intensity of therapy in a workforce population 2025 (Study)
- Arterial myeloperoxidase in the detection and treatment of vulnerable atherosclerotic plaque: a new dawn for an old light 2023 (Review)
- Role of myeloperoxidase in inflammation and atherosclerosis (Review) 2022 (Review)
- Unexpected Role of MPO-Oxidized LDLs in Atherosclerosis: In between Inflammation and Its Resolution 2022 (Review)
- Prognostic Role of Elevated Myeloperoxidase in Patients with Acute Coronary Syndrome: A Systemic Review and Meta-Analysis 2019 (Systematic Review)
Disclaimer
The MPO test is a cardiovascular risk marker, not a stand-alone diagnosis. A high result should be reviewed with a qualified clinician who can interpret it with symptoms, medical history, medications, blood pressure, lipid markers, glucose control, kidney function, and other inflammatory conditions. Seek urgent medical care for chest pain, severe shortness of breath, fainting, stroke-like symptoms, or sudden pain spreading to the arm, jaw, neck, back, or shoulder.
