Instalab

TMAO Test Blood

One of the strongest predictors of heart attack and stroke risk that your standard cholesterol panel completely misses.

Should you take a TMAO test?

This test is most useful if any of these apply to you.

Worried About Heart Disease
See whether your gut microbiome is quietly adding to your cardiovascular risk beyond what cholesterol tests reveal.
Already Managing Kidney Issues
Your kidneys clear this molecule, so tracking it helps gauge how kidney function is affecting your vascular risk.
Eating a Lot of Red Meat
Find out whether your diet and gut bacteria are producing levels linked to higher heart attack and stroke risk.
Healthy but Want to Stay Ahead
Get a baseline on a risk marker your standard panels miss, so you can track your trend as the science matures.

About TMAO

Your cholesterol numbers can look perfect and still leave you exposed. TMAO (trimethylamine N-oxide) is a metabolite your body produces from everyday foods, and it tracks a dimension of cardiovascular risk that lipid panels, blood sugar tests, and even inflammatory markers do not capture. In large studies following tens of thousands of people for over a decade, those with the highest TMAO levels faced roughly 30 to 60% greater risk of heart attack, stroke, and death, even after accounting for every traditional risk factor.

What makes TMAO unusual is that it sits at the intersection of three systems: your diet, your gut bacteria, and your kidneys. It is not a single organ's output. It is a composite signal reflecting how well those systems are working together, and whether they are quietly tilting your biology toward or away from vascular damage.

How Your Body Makes TMAO

When you eat foods rich in choline (eggs, liver), carnitine (red meat), or betaine, bacteria in your large intestine convert these nutrients into a gas called TMA (trimethylamine). TMA travels to your liver, where an enzyme called FMO3 (flavin-containing monooxygenase 3) converts it into TMAO. Your kidneys then clear most of the TMAO into your urine, typically within about 24 hours.

Fish is a special case. It contains preformed TMAO that gets absorbed directly into your bloodstream without needing gut bacteria to produce it. This is why eating fish can spike your TMAO temporarily, even though fish consumption is consistently linked to better heart health. This paradox is one of the reasons TMAO should never be interpreted on its own.

Heart Disease and Cardiovascular Events

The cardiovascular signal from TMAO is the most studied and the most consistent. A major meta-analysis pooling 44 cohorts and over 84,000 people found that higher TMAO was associated with about 29% higher risk of cardiovascular disease overall, 51% higher risk of cardiovascular death, and 30% higher risk of dying from any cause. These associations held after adjusting for the usual suspects: age, blood pressure, cholesterol, diabetes, and smoking.

In people who already have heart disease, the signal is even stronger. Among over 2,200 patients presenting with chest pain or acute coronary syndromes, those in the highest quarter of TMAO had roughly six times the odds of a major cardiovascular event within 30 days compared to those in the lowest quarter, and nearly double the risk of death over the following seven years. A separate analysis of patients after coronary stent procedures found that each 1 µM increase in TMAO was linked to about 9% higher risk of a future cardiovascular event.

If your TMAO comes back elevated alongside other concerning markers (high ApoB, elevated hs-CRP, or borderline blood sugar), that combination paints a much more complete picture of your vascular risk than any single number. If TMAO is the only marker that is elevated, a retest after dietary changes is a reasonable next step before escalating to further workup.

Heart Failure

In chronic heart failure, TMAO levels tend to be markedly elevated and predict worse outcomes. A study of over 3,200 heart failure patients (the BIOSTAT-CHF cohort) found that higher TMAO at baseline predicted death and rehospitalization over one to three years. An important finding from this study: standard heart failure medications (ACE inhibitors, beta-blockers, diuretics) improved the heart's pumping-strain marker BNP but did not lower TMAO, suggesting it reflects a separate biological process that standard therapy does not address.

Kidney Disease and Kidney Function

Because your kidneys are the main exit route for TMAO, kidney function is the single biggest determinant of your circulating level. As kidney filtration rate (eGFR) drops, TMAO accumulates. In a study of 521 people with chronic kidney disease (CKD), those in the highest quarter of TMAO had roughly twice the risk of dying over five years compared to those in the lowest quarter, even after adjusting for kidney function and inflammation.

The relationship runs both directions. In 440 people with type 2 diabetes, those in the highest third of TMAO (roughly 0.88 µM and above) faced about a six-fold increase in the risk of rapidly losing kidney function or reaching end-stage kidney disease. This makes TMAO particularly useful for anyone with early kidney concerns or diabetes: it can flag accelerating kidney trouble before standard kidney markers move.

Metabolic Health and Body Weight

TMAO is not just a cardiovascular marker. A dose-response meta-analysis found a positive, graded association between TMAO levels and body mass index (BMI) in apparently healthy adults. In a study of over 2,600 people across both clinical and population-based German cohorts, TMAO was independently associated with obesity and diabetes after adjusting for other risk factors. A separate cohort of over 2,000 diabetes-free Chinese adults followed for nearly nine years found that those in the highest third of baseline TMAO had 42% greater risk of developing type 2 diabetes.

The Fish Paradox and How to Read Your Result

One of the most common sources of confusion with TMAO is the fish effect. Eating fish raises TMAO far more acutely than eating red meat or eggs, sometimes by 40 to 60 times above baseline within hours. Yet fish consumption is consistently associated with lower cardiovascular risk. This is not actually contradictory once you understand the mechanism: fish delivers preformed TMAO that is rapidly cleared by the kidneys, while red meat provides carnitine that gut bacteria slowly and persistently convert into TMA. The chronic, bacteria-driven production from red meat appears to be the metabolically relevant signal, not the transient spike from fish.

This means a single TMAO reading taken the morning after a fish dinner can be misleading. For the most accurate picture, avoid fish for at least 24 hours before your blood draw.

Reference Ranges

There is no universally standardized clinical reference range for TMAO. The ranges below are drawn from large prospective cohorts and meta-analyses involving primarily middle-aged adults of European and Asian ancestry, measured by liquid chromatography-mass spectrometry (LC-MS). Your lab may report results in slightly different units or use different methods. Compare your results within the same lab over time for the most meaningful trend.

TierApproximate Range (µM)What It Suggests
Lower riskBelow 4Typical of healthy adults with normal kidney function and moderate meat intake. Aligns with the lowest-risk groups in prospective studies.
Moderate4 to 8Consistently associated with modestly higher cardiovascular event risk in large cohorts. Worth investigating alongside kidney function, diet, and other cardiometabolic markers.
Elevated8 to 20Often seen in older adults, people with early kidney dysfunction, or metabolic syndrome. Associated with meaningfully higher risk in multiple studies.
HighAbove 20Common in advanced kidney disease, heart failure, or combined diabetes and cardiovascular disease. Carries the strongest risk signal and warrants comprehensive evaluation.

Age strongly shifts the distribution: average levels rise from roughly 2.5 µM in younger adults to about 10 µM in older adults, partly reflecting declining kidney function. There are no well-validated sex-specific or ethnicity-specific cutpoints at this time.

When Results Can Be Misleading

TMAO is one of the more variable biomarkers you can order. Long-term within-person correlation is modest (around 0.25 in one large cohort with repeat measures seven years apart), meaning a single reading can be substantially different from your true average. The biggest confounders to watch for:

  • Recent fish intake: Fish can raise TMAO 40 to 60 times above baseline within hours. Avoid fish for at least 24 hours before your draw.
  • Kidney function: Even mild reductions in kidney filtration can raise TMAO significantly. Always interpret TMAO alongside eGFR or cystatin C.
  • Acute illness or surgery: TMAO levels shift during and after acute events like stroke or heart surgery, falling in the first 48 hours and then rebounding over weeks to months.
  • Broad-spectrum antibiotics: These can markedly suppress TMAO by wiping out the gut bacteria that produce TMA. If you have taken antibiotics in the past two to four weeks, your reading may be artificially low.

Tracking Your Trend

Because of TMAO's high day-to-day variability, a single reading is best treated as a starting point, not a verdict. If your result falls in the moderate or elevated range, a retest in three to six months (after making dietary changes and confirming stable kidney function) will tell you far more than the first number alone. If you are making deliberate shifts in your diet, like reducing red meat or increasing plant-based meals, a follow-up TMAO test is one of the few ways to see whether your gut microbiome is actually responding to those changes.

For ongoing monitoring, test at least annually if you have any cardiometabolic risk factors. If your levels are in the lower-risk range and your diet is stable, every one to two years is reasonable. The goal is to build a personal trend line rather than to react to any single data point.

What to Do With an Abnormal Result

If your TMAO comes back above 8 µM, start with context. Check your kidney function (eGFR or cystatin C) and recall what you ate in the 24 hours before your blood draw. If kidney function is normal and you did not eat fish recently, the elevation likely reflects a combination of your diet, your gut microbiome's composition, and your metabolic health.

Pair TMAO with a heart health panel (ApoB, hs-CRP, HbA1c, lipids) to see whether it fits into a broader pattern of elevated risk. If multiple markers are concerning, consider involving a cardiologist or lipidologist. If TMAO is isolated, dietary modification focused on reducing red meat and increasing fiber-rich plant foods is the most evidence-supported first step. Retest in three to six months to see if the change registered.

For results above 20 µM, kidney function should be evaluated thoroughly if it has not been already. This level is common in people with unrecognized kidney impairment, and addressing the underlying kidney issue will often bring TMAO down as well.

What Moves This Biomarker

Evidence-backed interventions that affect your TMAO level

↑ Increase
Eat a red meat-heavy diet (25% of calories from protein, primarily red meat)
Chronic red meat consumption more than doubled plasma and urine TMAO levels compared to white meat or plant protein diets over four weeks. The increase came from three mechanisms: more dietary precursors, greater microbial conversion of carnitine to TMA, and reduced kidney clearance of TMAO. When participants stopped eating red meat, their TMAO dropped back down within four weeks.
DietStrong Evidence
↓ Decrease
Follow a low-calorie DASH diet (rich in fruits, vegetables, whole grains, low-fat dairy)
A low-calorie DASH diet reduced TMAO by about 20 µM over 12 weeks in adults with obesity, roughly double the reduction seen with a standard low-calorie diet (which lowered TMAO by about 10.6 µM). The DASH pattern also reduced markers of gut-derived inflammation. If you are overweight and trying to lower TMAO, a DASH-style eating pattern appears more effective than calorie restriction alone.
DietStrong Evidence
↓ Decrease
Take a grape pomace polyphenol extract (Taurisolo, rich in resveratrol)
Four weeks of a grape pomace polyphenol supplement reduced TMAO levels by about 63.6% compared to only 0.54% in the placebo group. Polyphenols appear to work by inhibiting TMA-producing bacteria in the gut. This is one of the largest TMAO reductions seen in any human supplement trial, though the study was small and preliminary.
SupplementStrong Evidence
↓ Decrease
Replace animal meat with plant-based meat alternatives
Switching from animal meat to plant-based alternatives for eight weeks lowered average TMAO from 4.7 µM to 2.7 µM, a roughly 43% reduction. LDL cholesterol and body weight also decreased during the plant-based phase. This gives you a concrete dietary lever: substituting even two servings per day of plant-based protein for animal meat can meaningfully shift your TMAO.
DietModerate Evidence
↓ Decrease
Follow a Mediterranean eating pattern with low red meat intake (about 200g per week)
A Mediterranean-style diet with only about 200g of unprocessed red meat per week lowered fasting TMAO to 3.1 µM, compared to 5.0 µM on the same diet with 500g of red meat per week. The lower-meat version also showed a correlation between TMAO reduction and improved insulin resistance. Even within an already healthy eating pattern, the amount of red meat you include makes a measurable difference.
DietModerate Evidence
↓ Decrease
Take a synbiotic supplement (combination of probiotics and prebiotics)
Twelve weeks of synbiotic supplementation significantly reduced serum TMAO in patients with abnormal cholesterol levels. The reduction correlated with improvements in fasting blood glucose. Synbiotics may help by shifting the gut microbiome away from TMA-producing species. However, a separate trial in healthy young adults found no significant group-level TMAO reduction from a similar approach, suggesting the benefit may be greatest in people with metabolic dysfunction.
SupplementModerate Evidence
↓ Decrease
Take acarbose (an alpha-glucosidase inhibitor used for type 2 diabetes)
Six months of acarbose significantly reduced plasma TMAO in people with newly diagnosed type 2 diabetes, with a greater reduction than vildagliptin (another diabetes drug). The TMAO decrease correlated with improvements in BMI, waist circumference, and insulin resistance. If you have type 2 diabetes and are choosing between glucose-lowering medications, acarbose may offer the added benefit of lowering TMAO.
MedicationModerate Evidence
↓ Decrease
Supplement with dietary fiber alongside beef consumption
Two weeks of dietary fiber supplementation reduced TMAO production after eating beef, but only in people who habitually ate meat fewer than three times per week. Fiber also significantly reduced the abundance of a key bacterial gene (cutC) involved in TMA production. If you are a moderate or light meat-eater, adding fiber around meat-containing meals may help blunt the TMAO response.
DietModest Evidence
↓ Decrease
Take a water-soluble tomato extract (Fruitflow, polyphenol-rich)
Four weeks of a polyphenol-rich tomato extract lowered fasting plasma TMAO by about 1.5 µM from baseline and reduced urinary TMAO by about 19 µM. The extract also shifted gut microbiome composition. This represents a modest but real reduction, roughly equivalent to moving from the moderate to the lower-risk range for someone starting around 5 to 6 µM.
SupplementModest Evidence
↓ Decrease
Lose weight through caloric restriction combined with interval exercise
Two weeks of a 500-calorie-per-day deficit combined with interval exercise (60 minutes daily, alternating high and low intensity) reduced TMAO by about 31% in women with obesity, compared to a 32% increase in the group that exercised with a calorie-matched diet. The reduction was strongest in those who started with the highest TMAO. Caloric restriction appears to be the key driver, with exercise providing additive benefit.
LifestyleModest Evidence

Frequently Asked Questions

References

40 studies
  1. Gut Microbiota-derived TMAO: A Causal Factor Promoting Atherosclerotic Cardiovascular Disease?
    Marina Canyelles, C. Borràs, N. Rotllan, M. Tondo, J. Escolà-gil, F. Blanco-vacaInternational Journal of Molecular Sciences2023
  2. Implication of Trimethylamine N-oxide (TMAO) in Disease: Potential Biomarker or New Therapeutic Target
    M. H. Janeiro, M. Ramírez, F. Milagro, J. Martínez, M. SolasNutrients2018
  3. Gut Microbiota–dependent Trimethylamine N-oxide Predicts Risk of Cardiovascular Events in Patients With Stroke and is Related to Proinflammatory Monocytes
    A. Haghikia, Xinmin S Li, T. Liman, Nils Bledau, D. Schmidt, Friederike Zimmermann, N. Kränkel, C. Widera, K. Sonnenschein, S. Hazen, M. Endres, U. LandmesserArteriosclerosis, Thrombosis, and Vascular Biology2018
  4. Gut Microbiota Metabolites and Risk of Major Adverse Cardiovascular Disease Events and Death: A Systematic Review and Meta-analysis of Prospective Studies
    Yoriko Heianza, Wenjie Ma, J. Manson, K. Rexrode, L. QiJournal of the American Heart Association2017
  5. Microbiota-dependent Metabolite Trimethylamine-n-oxide is Associated With Disease Severity and Survival of Patients With Chronic Heart Failure
    M. Trøseid, T. Ueland, J. Hov, a. Svardal, Ida Gregersen, C. Dahl, S. Aakhus, E. Gude, B. Bjørndal, B. Halvorsen, T. Karlsen, P. Aukrust, L. Gullestad, Rolf K. Berge, a. YndestadJournal of Internal Medicine2015