Nitric oxide is a gas your body makes to relax blood vessels and keep blood flowing. It disappears within seconds of being made, so no blood test can catch it directly.1Lamkin Clinic. Nitric Oxide: Optimal Levels, Assessment & Cardiovascular Interpretation What a “nitric oxide blood test” really reports is what the gas leaves behind, an indirect trace rather than the molecule itself. That means the number can move for reasons that have nothing to do with how much nitric oxide your vessels are making, from your lunch to your kidneys.
Nitrite and Nitrate, the Breakdown Products Your Lab Counts
Nitric oxide lasts only about 2 to 6 seconds in the blood before reacting with oxygen.2Lamkin Clinic. Nitric Oxide: Optimal Levels, Assessment & Cardiovascular Interpretation It turns first into nitrite and then into nitrate, and both stay around much longer.3Lamkin Clinic. Nitric Oxide: Optimal Levels, Assessment & Cardiovascular Interpretation So labs estimate how much nitric oxide your body is making from the amount of nitrite and nitrate in the sample.4PubMed Central. Measuring Nitrite and Nitrate, Metabolites in the Nitric Oxide Pathway, in Biological Materials using the Chemiluminescence Method Your report may say “NOx,” which is simply nitrite and nitrate added together. Some labs report the two separately, often using a color-changing chemical test for nitrite.5PubMed. Age-associated changes in nitric oxide metabolites nitrite and nitrate
Results are usually given in micromoles per liter, written µmol/L or µM. Nitrite is usually a much smaller number than nitrate, so the total is mostly nitrate. That is because nitrite is the earlier, shorter-lived product, and nitrate is the end product that accumulates. Nitrate also comes from two places: the body’s own nitric oxide and the food you eat. Total NOx blends both, and the lab can’t separate them. Bacteria on the tongue even make nitrite from nitrate, so the two substances sit in a loop rather than acting as independent measures.
Much of the nitric oxide in blood isn’t captured by a standard NOx test at all. Free nitric oxide in plasma is found only in tiny amounts, around 3 billionths of a mole per liter.6PubMed. Nitric oxide circulates in mammalian plasma primarily as an S-nitroso adduct of serum albumin But plasma holds about 2,000 times more nitric oxide bound to proteins, mostly albumin, the main protein in blood.7PubMed. Nitric oxide circulates in mammalian plasma primarily as an S-nitroso adduct of serum albumin That bound form works like a storage tank the body draws on to keep vessels relaxed.8PubMed. Nitric oxide circulates in mammalian plasma primarily as an S-nitroso adduct of serum albumin Red blood cells also carry nitric oxide on hemoglobin and release it where oxygen runs low, widening vessels there.9PubMed Central. Nitric oxide, vasodilation and the red blood cell A nitrite-and-nitrate result therefore shows only part of the picture.
What a Normal Result Looks Like
- Healthy adults aged 25 to 55: about 21 µmol/L on average, with most people roughly 8 to 34 µmol/L.10PubMed. Biological reference interval of nitric oxide in health and disease
- Healthy non-smoking men and women in a general population: about 24 to 25 µmol/L on average.11PubMed. Serum nitric oxide metabolite levels in a general healthy population: relation to sex and age
- Women aged 25 to 35 before menopause: about 13 µmol/L on average.12PubMed. Biological reference interval of nitric oxide in health and disease
- Women aged 40 to 55 after menopause: about 10 µmol/L on average.13PubMed. Biological reference interval of nitric oxide in health and disease
- Healthy pregnant women aged 25 to 35: about 71 µmol/L on average.14PubMed. Biological reference interval of nitric oxide in health and disease
Age and sex nudge the number. In young adults in their 20s, men tend to run slightly higher than women, about 25 versus 23 µmol/L.15PubMed. Serum nitric oxide metabolite levels in a general healthy population: relation to sex and age Levels in both men and women tend to peak in the 50s.16PubMed. Serum nitric oxide metabolite levels in a general healthy population: relation to sex and age Women with higher levels tended to be older, heavier, and to have higher fasting blood sugar.17PubMed. Serum nitric oxide metabolite levels in a general healthy population: relation to sex and age Pregnancy raises levels several times over as part of the body’s normal changes, so a high result in pregnancy isn’t on its own a warning sign. Always compare your result with the range printed on your own report, since labs and methods differ. Labs use different chemical methods and the groups studied differ in age, diet, and sex mix, so there is no single universal normal number for NOx.
To read your own number, check whether the report’s reference range names the group it was built from, such as adults generally or a specific age band or sex. A range from a mixed group may fit you poorly. Ask which method the lab used, since the printed range only applies to results produced by that same method. If a value falls far outside the range, the useful next step is usually to repeat the test under the same conditions rather than draw conclusions from the first result.
What Can Push Your Number Up or Down
Eating nitrate-rich foods raises nitrite and nitrate in blood, saliva, and urine.18PubMed. Influence of dietary nitrate food forms on nitrate metabolism and blood pressure in healthy normotensive adults Beetroot, spinach, lettuce, celery, and arugula are among the richest sources. A salad or beet juice the day before can lift your result even though your vessels haven’t changed.
The test can’t tell nitrate from your lunch apart from nitrate made by your vessels, so one reading says little on its own. Blood nitrate rises after a nitrate-rich meal and then drifts back down over hours to days, so the timing of your last salad relative to the blood draw matters. Fasting doesn’t fully remove the effect of the previous day’s meals. Cured meats can add to your intake too, because of their preservatives, though vegetables are the larger source for most people.
Your kidneys clear nitrate from the blood into urine. So in people with kidney failure on dialysis, average levels were about 99 µmol/L, roughly four times the 22 µmol/L seen in healthy people.19PubMed Central. Nitric Oxide Levels in Patients with Chronic Renal Disease The worse kidney function was, as shown by higher creatinine, the higher the level rose.20PubMed Central. Nitric Oxide Levels in Patients with Chronic Renal Disease A high result in someone with kidney disease mostly reflects slower clearance, not extra nitric oxide. If your kidney function has recently changed, NOx results from before and after the change aren’t comparable, because the kidneys’ clearance rate shifts the baseline.
How the blood sample is handled can also change the reading. Leaving blood at room temperature can push measured levels up in plasma and down in whole blood.21PubMed Central. Artifacts Introduced by Sample Handling in Chemiluminescence Assays of Nitric Oxide Metabolites Freezing and thawing a sample can turn one form into another.22PubMed Central. Artifacts Introduced by Sample Handling in Chemiluminescence Assays of Nitric Oxide Metabolites Some common tube additives, including the anticoagulant EDTA, can break down bound forms of nitric oxide.23PubMed Central. Artifacts Introduced by Sample Handling in Chemiluminescence Assays of Nitric Oxide Metabolites
What the Result Can and Can’t Say About Your Heart and Blood Vessels
Nitric oxide is made by the thin lining of your blood vessels. The lining senses forces like blood flow and chemical signals, and responds by making the gas. It moves into the muscle layer of the vessel wall and tells those muscle cells to relax. The vessel widens, blood flows more easily, and pressure falls.
When the lining stops making enough nitric oxide, the condition is a key risk factor for high blood pressure and heart disease.24PubMed Central. Nitric Oxide in Hypertension Mice missing the gene for the vessel-lining enzyme that makes nitric oxide have higher blood pressure.25PubMed Central. Nitric Oxide in Hypertension In animals, higher blood nitrite went along with lower blood pressure.26PubMed Central. Circulating Blood eNOS Contributes to the Regulation of Systemic Blood Pressure and Nitrite Homeostasis
That doesn’t mean a blood test settles the question for you. A natural blood substance blocks the enzyme that makes nitric oxide and can tighten blood vessels.27PubMed. Asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, explains the “L-arginine paradox” and acts as a novel cardiovascular risk factor Higher levels of it may be one way the vessel lining becomes damaged.28PubMed Central. The Role of Asymmetric Dimethylarginine (ADMA) in Endothelial Dysfunction and Cardiovascular Disease The vessel effect of nitroglycerin, a common heart medicine, may not even depend on raising nitric oxide levels at normal doses.29PubMed. Does nitric oxide mediate the vasodilator activity of nitroglycerin?
Someone could make normal amounts of nitric oxide and still have stiff vessels if the muscle responds poorly, and a NOx result wouldn’t reveal that. Because food adds nitrate, a person with impaired vessel lining could even show a normal or high NOx after a vegetable-rich meal, which would falsely reassure.
Doctors judge vessel health with blood pressure, cholesterol, blood sugar, and sometimes ultrasound of artery widening rather than an NOx test. If a wellness clinic tells you your nitric oxide is “low,” that doesn’t diagnose high blood pressure or heart disease. Ask whether your diet before the test and the sample handling were accounted for, and get the standard checks. A low reading isn’t on its own a reason to buy supplements.
Where Specialists Do Use Nitric Oxide Measurements
Pulmonary hypertension means high pressure in the arteries carrying blood from the heart to the lungs, which makes the heart work harder and can lead to heart failure. In people with an unexplained form of it, blood NOx was lower than in healthy people.30PubMed. Profiling nitric oxide metabolites in patients with idiopathic pulmonary arterial hypertension Lower levels went with higher lung artery pressure and a weaker heart output.31PubMed. Profiling nitric oxide metabolites in patients with idiopathic pulmonary arterial hypertension In one study, patients with NOx at or below 10 µmol/L had markedly worse survival.32PubMed. Profiling nitric oxide metabolites in patients with idiopathic pulmonary arterial hypertension Levels also fell the longer people had lived with the disease.33PubMed. Biochemical reaction products of nitric oxide as quantitative markers of primary pulmonary hypertension Lower NOx in these patients is a marker linked to severity, which doesn’t by itself show that low nitric oxide caused the illness.
Sepsis shows the opposite pattern. It is the body’s dangerous reaction to infection, and the immune response switches on enzymes that make large amounts of nitric oxide, unlike the normal steady supply from the vessel lining. Those huge bursts help drive the sharp blood pressure drop of septic shock.34PubMed Central. Nitric oxide in sepsis: pathophysiological mechanisms and therapeutic implications The surge widens vessels throughout the body, so organs may not receive enough blood.
In diabetic men with erectile dysfunction, lower nitric oxide levels in blood went with more severe problems.35PubMed. Diagnostic value of nitric oxide, lipoprotein(a), and malondialdehyde levels in the peripheral venous and cavernous blood of diabetics with erectile dysfunction Blood from an arm vein showed the same pattern as blood from the penis, pointing to a whole-body blood vessel issue.36PubMed Central. Markers of erectile dysfunction These findings are mainly used in studies, not yet as a routine diagnostic test.
In studies, levels differ on average between sick and healthy groups, but individual results overlap heavily between them. Where specialists use NOx at all, they read it alongside scans and pressure measurements, never alone.
Blood Test, Breath Test, or Saliva Strip
The breath nitric oxide test, often called FeNO, measures nitric oxide gas you breathe out, which comes from inflamed airways. It’s commonly used to help diagnose and manage asthma. In people with COPD, a reading above 25 parts per billion helped spot those who also have asthma features.37PubMed Central. Clinical utility of fractional exhaled nitric oxide and blood eosinophils counts in the diagnosis of asthma–COPD overlap That cutoff caught only about 6 in 10 such people, so it supports rather than replaces a doctor’s judgment.38PubMed Central. Clinical utility of fractional exhaled nitric oxide and blood eosinophils counts in the diagnosis of asthma–COPD overlap
The test is quick and needs no needle. You breathe out steadily into a handheld device for several seconds, and it reports the result in parts per billion in the clinic. Nitrate-rich food shortly before can slightly affect breath readings, so the clinic may ask about recent meals.
The breath test and the blood test answer different questions. The breath test looks at gas made by inflamed airway cells, so it speaks to lung inflammation, whereas the blood test reflects nitric oxide products from the whole body. A high breath result points toward a type of airway inflammation that often responds to inhaled steroids, which is why it helps guide asthma care. A normal reading doesn’t rule out asthma, so doctors combine it with symptoms and breathing tests.
Home saliva strips sold with supplements measure nitrite in saliva. But saliva nitrite didn’t track blood nitrite at all,39PubMed Central. The Relationship between Plasma and Salivary NOx and saliva levels shot up after nitrate-rich meals.40PubMed. Influence of dietary nitrate food forms on nitrate metabolism and blood pressure in healthy normotensive adults A strip mainly shows what you recently ate, not your blood vessel health.
How to Prepare If You’re Having the Blood Test
Ask whether to avoid nitrate-rich vegetables, beet juice, and cured meats for a day or so before, since food raises blood levels.41PubMed. Influence of dietary nitrate food forms on nitrate metabolism and blood pressure in healthy normotensive adults Skipping a big nitrate-heavy meal the evening before is simpler than overhauling your whole diet. If you plan a repeat test, follow the same food pattern both times so any difference isn’t merely from meals.
Tell the person ordering the test about kidney disease, which can raise levels several times over.42PubMed Central. Nitric Oxide Levels in Patients with Chronic Renal Disease Mention recent illness or dehydration too, because kidney function can temporarily change and shift the result. If you are pregnant or might be, say so.
Bring a list of every medicine and supplement you take, including over-the-counter “nitric oxide” products, since some contain nitrate or related compounds. Pause nitrate supplements only if the ordering clinician agrees, and never stop prescribed heart medicine on your own.
The draw itself is an ordinary arm-vein draw, often after fasting. Results may take days, since many labs send it out. Ask that the sample be processed promptly, since standing at room temperature can distort it.43PubMed Central. Artifacts Introduced by Sample Handling in Chemiluminescence Assays of Nitric Oxide Metabolites Use the same lab and the same preparation for any repeat test.
When the result comes back, ask which range it was compared against, and whether it fits your age and sex. Ask whether diet or your kidneys could explain it, and what decision this number would actually change for you.