Test Summary
TMAO (Trimethylamine N-Oxide)
Test Code: 94154
Clinical use
- Assess gut microbiota contribution to risk of a major adverse cardiovascular event (MACE)
Clinical background
An important step for reducing risk of cardiovascular disease (CVD) is to identify and treat known risk factors (eg, smoking, dyslipidemia, hypertension, poor diet). Emerging risk factors, such as the gut microbiota–dependent metabolite trimethylamine N-oxide (TMAO), may help refine risk assessment and may also represent new targets for therapeutic intervention.
Circulating TMAO is implicated in various pathophysiological processes involved in atherosclerosis and CVD.1 TMAO is generated through (1) direct intake of trimethylamine (TMA) and TMAO, which are abundant in fish and other seafood, and (2) metabolism of dietary precursors such as phosphatidylcholine (also known as lecithin), choline, betaine, and L-carnitine, which are found in red meat, egg yolks, dairy products, energy drinks, and some supplements.2–4 Gut bacteria convert these precursors into TMA, which is subsequently oxidized to TMAO in the liver. Circulating TMAO increases atherosclerosis-causing foam cells, inhibits transport of cholesterol from tissues to the liver, and increases thrombotic risk by altering platelet properties, which can lead to the development of cardiometabolic diseases.1
In patients with high risk for CVD or existing comorbid disease, high levels of circulating TMAO are associated with increased risk of CVD and mortality, independent of other risk factors. An umbrella review of 24 meta-analyses of clinical studies found that higher TMAO levels were associated with higher risk of MACE (myocardial infarction, stroke, or cardiovascular death), hypertension, diabetes mellitus, all-cause mortality, and CVD mortality (Table).5
Table. Health Outcomes Associated With High TMAO Levels
Outcome |
Participants5,a |
Fold-increased risk (95% CI)5,b |
MACE |
39,314 |
HR, 1.65 (1.45-1.88) |
Hypertension |
18,854 |
RR, 1.40 (1.13-1.72) |
Diabetes mellitus |
22,999 |
OR, 1.71 (1.35-2.18) |
All-cause mortality |
38,862 |
HR, 1.56 (1.38-1.77) |
CVD mortality |
11,296 |
HR, 2.00 (1.72-2.33) |
| CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; MACE, major adverse cardiovascular event; OR, odds ratio; RR, risk ratio; TMAO, trimethylamine N-oxide. | |
| a | Cohorts consisted primarily of patients with a history of CVD, stroke, heart failure, diabetes mellitus, or chronic kidney disease. |
| b | For high versus low TMAO levels as defined by cutoffs in the studies comprising the meta-analyses. This analysis included only prospective cohort studies that adjusted for renal function. |
Quest Diagnostics and Cleveland HeartLab offer the TMAO (Trimethylamine N-Oxide) test (test code 94154) to assess the risk of MACE in individuals with intermediate to high risk of CVD. The American College of Cardiology/American Heart Association guidelines on cardiovascular risk assessment define intermediate 10-year risk as 7.5% to <20% and high 10-year risk as ≤20%.6,7 These risk scores are based on race- and sex-specific pooled cohort equations and can be estimated using an online calculator (tools.acc.org/ascvd-risk-estimator-plus).
Clinicians and researchers continue to define the utility of TMAO testing to guide dietary modifications and therapy.1,2
Individuals suitable for testing
- Individuals who have intermediate to high risk of CVD
Method
- Liquid chromatography-tandem mass spectrometry
- Analytical sensitivity: 0.27 μM
- Analytical specificity: assay is specific for TMAO
- Reportable ranges: 0.27 μM to 267 μM
Interpretive information
In patients with an intermediate or high risk of CVD, a TMAO level of 8
- <6.2 μM defines a population at lower risk for MACE relative to those with higher TMAO levels
- 6.2 μM to 9.9 μM indicates a moderately high risk of MACE (2-fold increase at 3 years) relative to those with TMAO levels <6.2 μM
- ≥10 μM (ie, greater than the upper limit of the Cleveland HeartLab 95% population interval) indicates a high risk of MACE relative to those with TMAO levels <6.2 μM, given the dose-dependent relationship between TMAO and MACE risk demonstrated across multiple clinical subgroups9
TMAO levels may increase within 15 minutes of fish consumption10 and remain elevated for 12 to 24 hours,11 but such acute elevation has not been associated with increased risk of MACE.10 Consequently, in addition to fasting, patients are required to avoid consumption of fish, fish oil, and krill oil for up to 24 hours before having their TMAO levels tested.
Elevated levels of TMAO are observed in patients after bariatric surgery.12 No TMAO-associated increased risk of MACE has been reported in these patients.
References
- Shanmugham M, Bellanger S, Leo CH. Gut-derived metabolite, trimethylamine-N-oxide (TMAO) in cardio-metabolic diseases: detection, mechanism, and potential therapeutics. Pharmaceuticals. 2023;16(4):504. doi:10.3390/ph16040504
- Jaworska K, Kopacz W, Koper M, et al. Microbiome-derived trimethylamine N-oxide (TMAO) as a multifaceted biomarker in cardiovascular disease: challenges and opportunities. Int J Mol Sci. 2024;25(23):12511. doi:10.3390/ijms252312511
- Wilcox J, Skye SM, Graham B, et al. Dietary choline supplements, but not eggs, raise fasting TMAO levels in participants with normal renal function: a randomized clinical trial. Am J Med. 2021;134(9):1160-1169.e3. doi:10.1016/j.amjmed.2021.03.016
- Jagim AR, Harty PS, Barakat AR, et al. Prevalence and amounts of common ingredients found in energy drinks and shots. Nutrients. 2022;14(2):314. doi:10.3390/nu14020314
- Li D, Lu Y, Yuan S, et al. Gut microbiota–derived metabolite trimethylamine-N-oxide and multiple health outcomes: an umbrella review and updated meta-analysis. Am J Clin Nutr. 2022;116(1):230-243. doi:10.1093/ajcn/nqac074
- Goff DC, Lloyd-Jones DM, Bennett G, et al. 2013 ACC/AHA guideline on the assessment of cardiovascular risk. Circulation. 2014;129(25 suppl 2):S49-S73. doi:10.1161/01.cir.0000437741.48606.98
- Arnett DK, Blumenthal RS, Albert MA, et al. 2019 ACC/AHA guideline on the primary prevention of cardiovascular disease. Circulation. 2019;140(11):e596-e646. doi:10.1161/cir.0000000000000678
- Tang WHW, Wang Z, Levison BS, et al. Intestinal microbial metabolism of phosphatidylcholine and cardiovascular risk. N Engl J Med. 2013;368(17):1575-1584. doi:10.1056/nejmoa1109400
- Heianza Y, Ma W, Manson JE, et al. Gut microbiota metabolites and risk of major adverse cardiovascular disease events and death: a systematic review and meta-analysis of prospective studies. J Am Heart Assoc. 2017;6(7):e004947. doi:10.1161/jaha.116.004947
- Cho CE, Taesuwan S, Malysheva OV, et al. Trimethylamine-N-oxide (TMAO) response to animal source foods varies among healthy young men and is influenced by their gut microbiota composition: A randomized controlled trial. Mol Nutr Food Res. 2017;61(1). doi:10.1002/mnfr.201600324
- Wang Z, Tang WHW, O’Connell T, et al. Circulating trimethylamine N-oxide levels following fish or seafood consumption. Eur J Nutr. 2022;61(5):2357-2364. doi:10.1007/s00394-022-02803-4
- Jamialahmadi T, Simental-Mendia LE, Zengin G, et al. Meta-analysis of the impact of bariatric surgery on circulating TMAO levels as a predictor of cardiovascular disease risk. Curr Med Chem. 2024;31(24):3791-3797. doi:10.2174/0929867330666230523155750
Content reviewed 04/2025
94154 - TMAO (Trimethylamine N-Oxide)
Reference ranges are provided as general guidance only. To interpret test results use the reference range in the laboratory report.
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