Myeloperoxidase (MPO)
An enzyme released by activated white blood cells within arterial plaque, promoting oxidative damage and plaque instability.
Where Lp-PLA2 indicates plaque inflammation, MPO indicates plaque vulnerability — the tendency to rupture, which is what actually causes heart attacks. Complements the structural markers.
Three statements worth having in one place. A consensus standard assay has not been established. No guideline recommends MPO for cardiac risk assessment. And in the chest-pain setting where it was most studied, it does not yet appear to provide additional prognostic information for the evaluation of individual patients on top of troponin. That is not a reason to dismiss the biology — MPO is a real mechanism in plaque — it is a reason not to act on your number.
Check a Myeloperoxidase (MPO) result against this range →
What Myeloperoxidase (MPO) actually measures — the analyte, and the assay
Two completely different tests are called MPO, and a reader holding a result has no way to tell which one they have. That is the most useful sentence on this page, so it goes first.
- Myeloperoxidase mass, an immunoassay measuring how much of the enzyme is circulating, reported in ng/mL or pmol/L. This is the cardiovascular test.
- Anti-MPO ANCA, an autoantibody against the enzyme, reported as units or a titre. It is an autoimmune test used in the workup of small-vessel vasculitis, and it says nothing whatever about plaque Walulik 2023 Merindol 2023.
The enzyme itself is a hematology protein first. Myeloperoxidase is a heme-containing homodimer of about 150 kDa stored in the azurophilic granules of neutrophils, where it makes up a remarkable share of total cell protein, and in monocyte granules. Its reaction is the one that gives neutrophils their chemical weapon: hydrogen peroxide plus chloride to hypochlorous acid, the same oxidant as household bleach, generated inside a phagosome Siraki 2021 Rizo-Tellez 2022. It also has substantial non-enzymatic signaling roles, which is why the literature keeps widening rather than settling Kargapolova 2021.
Which makes the sample tube part of the measurement, more than for almost anything else on this site. The enzyme lives inside white cells and is bound to the vessel wall, so any process that degranulates neutrophils or strips the endothelium releases it. Clotting a sample degranulates neutrophils, so serum reads differently from plasma; heparin displaces endothelium-bound enzyme into the circulation. The landmark chest-pain study measured plasma MPO for exactly this reason Brennan 2003.
And there is no shared standard. Mass immunoassays and enzyme activity assays measure different quantities, no consensus reference method exists, and a number from one platform cannot be read against a cut-point from another. This is not a small caveat — it is why no guideline recommends the test.
Myeloperoxidase (MPO): what changes the blood, and what only changes the reading
What changes the myeloperoxidase in your blood:
- How many neutrophils you have, and how activated they are. MPO is a neutrophil product, so the count on your CBC is the first-order determinant. Anything that raises neutrophils raises the substrate for this measurement Rizo-Tellez 2022.
- Acute exercise. Neutrophils demarginate and degranulate with hard work, so a draw within a day or two of a heavy session is measuring training rather than vasculature.
- Smoking, which is both the largest modifiable driver of neutrophil activation in most populations and the intervention this page's own advice leads with.
- Infection and any inflammatory illness, since MPO release is part of the normal innate response and not a vascular signal Siraki 2021.
- Neutrophil extracellular trap formation. NETs carry MPO on their DNA scaffold, they are implicated in cardiovascular and inflammatory disease Klopf 2021, and in people who have had a venous thromboembolism, neutrophil activation and circulating NET markers stay raised for at least one year after the event Zapponi 2022.
- Genetic myeloperoxidase deficiency, which is one of the commoner inherited neutrophil abnormalities, is usually asymptomatic, and would make this test permanently and meaninglessly low Siraki 2021.
What changes only the reading — and on this marker the analytical list dominates the biological one:
- Serum versus plasma, and which anticoagulant. Clotting releases enzyme from the white cells in the tube; heparin releases it from the vessel wall in the patient Brennan 2003.
- Time before centrifugation, since leukocytes left sitting in contact with plasma keep contributing enzyme that was intracellular at the moment of the draw.
- Which assay, and whether it measured mass or activity. With no reference method, these are not versions of one number Kargapolova 2021.
- Freeze-thaw cycles, which matter for a stored specimen and are invisible on the report.
- Confusing the result with an ANCA, which is a reader-side error rather than a laboratory one, and the commonest one this marker produces Walulik 2023.
Reference interval or decision threshold — which kind of number Myeloperoxidase (MPO) is
Neither, honestly. The number printed beside an MPO result is a manufacturer's reference interval for one platform, derived from whichever samples that manufacturer measured. It is not a decision threshold, because no guideline body has set one, and it is barely a reference interval, because without a consensus assay it does not transfer to any other laboratory.
The evidence that made the test famous is real, and is narrower than it is remembered as being. In patients presenting to hospital with chest pain, initial plasma myeloperoxidase predicted subsequent myocardial infarction even in those who were troponin T negative (P < 0.001), and baseline concentrations independently predicted major adverse coronary events at 30 days Brennan 2003. That is a finding about people in an emergency department with symptoms — not about a well person on a wellness panel, which is the population reading this page.
The mechanistic case is coherent, which is what keeps the marker alive. Hypochlorous acid modifies apolipoprotein A-I and impairs cholesterol efflux, MPO-derived oxidants consume nitric oxide, and the enzyme is present and active in atherosclerotic plaque Frangie 2022 Siraki 2021. A plausible mechanism is not an outcome-anchored threshold, and the gap between those two is where this marker sits.
So there is no optimum to state and this page should not invent one. What the number can legitimately do is track a driver you are already treating — smoking, periodontal inflammation, visceral adiposity — in a person whose neutrophil count is stable and whose samples are collected identically. That is a much smaller claim than ‘plaque vulnerability’, and it is the one the evidence supports.
How you would know your Myeloperoxidase (MPO) was wrong — and when to redraw
The clock is the neutrophil's, and it is measured in hours. A circulating neutrophil's residence time is short, and MPO is its cargo, so this marker reflects the state of the granulocyte pool over about the last day. It is not an integrating measure of anything, which rules out using it the way HbA1c or ferritin are used.
Practical intervals. No retest inside six months unless a specific driver is being treated, because nothing about atherosclerosis changes faster than that and everything about neutrophil activation changes far faster. After stopping smoking or treating periodontal disease, three months. Never within 72 hours of hard training or a viral illness.
Conditions that must match, and they matter more here than the interval does: the same laboratory and the same assay, since no reference method exists Kargapolova 2021; the same specimen type, serum or plasma, with the same anticoagulant Brennan 2003; the same time from draw to spin; and a stable neutrophil count on the CBC.
What would have to change for the second value to mean something. Because MPO has no threshold, the only interpretable result is a pattern across markers that do:
- MPO up with the neutrophil count up on the CBC? That is white cell traffic, not plaque. Repeat when the count is back to baseline Rizo-Tellez 2022.
- MPO up with hs-CRP up? A systemic inflammatory process is the parsimonious explanation, and MPO adds nothing the CRP did not already say Siraki 2021.
- MPO up with hs-CRP and neutrophils both normal? Only now is the vascular question on the table — and it is answered by ApoB and Lp(a), which have thresholds, rather than by repeating this Frangie 2022.
- MPO persistently very low? Consider inherited myeloperoxidase deficiency before concluding that a protocol worked Siraki 2021.
What Myeloperoxidase (MPO) cannot tell you
It cannot tell you a plaque is unstable. Plaque vulnerability is a structural property of an artery, and no circulating enzyme concentration establishes it in an individual. The mechanistic link is well described Frangie 2022; the individual-level inference is not.
It cannot separate vascular MPO from every other source. The enzyme in your plasma came from neutrophils, and neutrophils degranulate in gum disease, a chest infection, a hard session and the collection tube Rizo-Tellez 2022 Klopf 2021.
It cannot be compared between laboratories, or across a platform change at one. There is no consensus standard assay, so a series is only a series if nothing about the method moved Kargapolova 2021.
It is not the ANCA test, and the ANCA test is not this. Anti-MPO antibodies are a marker of small-vessel vasculitis with their own titre-dependent diagnostic significance Merindol 2023, and confusing the two is the single most consequential misreading available on this page Walulik 2023.
The wrong inference readers actually draw is that a raised MPO means their plaque is about to rupture, and a normal one means it is not. Neither conclusion is supported. The finding that made the marker's name was made in symptomatic patients in hospital, at 30 days Brennan 2003 — and the honest use of the test on a wellness panel is as a prompt to go and deal with the smoking, the gums and the visceral fat, all of which were worth dealing with before anyone drew the tube.
Sources read for these sections
- Siraki AG. The many roles of myeloperoxidase: From inflammation and immunity to biomarkers, drug metabolism and drug discovery. Redox Biology 2021 · PMID 34455146
- Kargapolova Y, et al. The Enzymatic and Non-Enzymatic Function of Myeloperoxidase (MPO) in Inflammatory Communication. Antioxidants 2021 · PMID 33916434
- Rizo-Tellez SA, et al. Myeloperoxidase: Regulation of Neutrophil Function and Target for Therapy. Antioxidants 2022 · PMID 36421487
- Frangie C, et al. Role of myeloperoxidase in inflammation and atherosclerosis (Review). Biomedical Reports 2022 · PMID 35620311
- Brennan ML, et al. Prognostic value of myeloperoxidase in patients with chest pain. New England Journal of Medicine 2003 · PMID 14573731
- Walulik A, et al. The Role of Neutrophils in ANCA-Associated Vasculitis: The Pathogenic Role and Diagnostic Utility of Autoantibodies. International Journal of Molecular Sciences 2023 · PMID 38139045
- Merindol J, et al. Diagnostic significance of antineutrophil cytoplasmic antibody (ANCA) titres: a retrospective case-control study. RMD Open 2023 · PMID 37055171
- Klopf J, et al. Neutrophil Extracellular Traps and Their Implications in Cardiovascular and Inflammatory Disease. International Journal of Molecular Sciences 2021 · PMID 33429925
- Zapponi KCS, et al. Neutrophil activation and circulating neutrophil extracellular traps are increased in venous thromboembolism patients for at least one year after the clinical event. Journal of Thrombosis and Thrombolysis 2022 · PMID 34449018
Where to start with Myeloperoxidase (MPO)
In this order. Start at the supplement and you learn nothing, because you never established the number was real.
You have the range, where it came from and the first two moves. Inside is the rest of the five-pathway protocol — supplements, hormones, peptides — the order to run them in, and what to change when the number will not move.
Get the full protocol — $10/mo →📚 Brennan ML et al., NEJM 2003 — MPO and cardiovascular risk prediction.
🩸 Test your Myeloperoxidase (MPO)
Order directly through Marek Diagnostics — no doctor's visit needed, drawn at any Quest location in the US. Code CAMERON applies 10% off automatically.
Order this test — 10% off → Browse all 103 markers →What Myeloperoxidase (MPO) is usually tested alongside
One marker is a data point. These panels add the markers that make Myeloperoxidase (MPO) interpretable, name why each is on the list, and load the set into your cart at 10% off.
includes this + 9 more markers — Persistent aches, slow recovery, autoimmune history, high cardiovascular risk, or a raised CRP that nobody explained.
What people use Myeloperoxidase (MPO) to decide
Nobody orders a test for its own sake. Myeloperoxidase (MPO) is on the test list for these pathways — each one links to what the pathway claims, and what its test list is read for before you spend anything on it.
ADMA inhibits nitric oxide synthase directly, so it is the most specific endothelial marker available. Dysfunction here precedes visible plaque by decades.
Measure Lp(a) once in your life. It is genetic, unmoved by diet or exercise, raised in about one in five people, and almost never ordered — and it changes how aggressively everything else on this page should be treated.
Would you feel it? Symptoms Myeloperoxidase (MPO) helps explain
People search for how they feel, not for a marker. These are the complaints where this one is worth checking, and whether it is first-line or a follow-up.
Why your Myeloperoxidase (MPO) might be wrong
Most abnormal results are interference, not disease. Check these before you change anything. Each says whether the number is wrong (repeat it), badly timed (redraw it), or real with a cause.
MPO comes from neutrophils, so anything activating them — infection, recent injury, smoking — raises it independently of plaque.
Draw when well and away from illness by two weeks.
Red cells rupturing in the tube spill their contents into the serum. Potassium, LDH, AST and magnesium are far higher inside cells than outside, so a hemolyzed sample reports them falsely high. Caused by a difficult draw, a narrow needle, or shaking the tube.
The lab usually flags it. If your result is odd and the report mentions hemolysis, that is your answer — repeat the draw.
What Myeloperoxidase (MPO) means in combination
One marker tells you a little; combinations tell you the story. These are the named patterns this one takes part in.
Residual inflammatory risk. Plaque forms and destabilizes through inflammation as well as lipids, so hitting an ApoB target while CRP stays high leaves a meaningful part of the risk untouched.
Rule out the obvious first — CRP rises with any infection, injury or hard training, so retest rested and well. If it stays up: sleep, visceral fat, periodontal disease, gut health, omega-3s. Persistent unexplained elevation deserves a real workup.
What to test next
These put Myeloperoxidase (MPO) in context — each with its own full breakdown.
Frequently asked questions
<470 pmol/L (assay dependent). Ranges vary by laboratory and assay — always compare to the range printed on your own report.
No validated cut-point exists - the assay is not standardized and no guideline recommends MPO for cardiac risk. Payer technology assessment of myeloperoxidase immunoassay, citing the absence of guideline support.
Associated with vulnerable plaque and increased risk of acute coronary events.
Favorable.
You can order Myeloperoxidase (MPO) directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.
Where this goes next
This page is the free framework. The protocol itself — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.