Vitamin B1 (Thiamine) Plasma/Serum LC–MS/MS Biomarker Testing
It measures thiamine (vitamin B1) in your blood to help assess deficiency risk and monitoring, with easy ordering and Quest lab access via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
This test measures vitamin B1 (thiamine) in your blood using a highly specific method (LC–MS/MS). Thiamine is essential for turning carbohydrates into usable energy and for normal nerve and heart function.
A low result can fit with symptoms like fatigue, numbness or tingling, weakness, poor appetite, or brain fog, but symptoms are not specific. Your result is most useful when it is interpreted alongside your diet, medications, medical history, and other labs.
Because thiamine deficiency can develop in certain higher-risk situations, testing can help you and your clinician decide whether you need treatment, monitoring, or a broader nutrition workup. This article is educational and does not diagnose a condition on its own.
Do I need a Vitamin B1 (Thiamine) Plasma/Serum LC–MS/MS test?
You may want a thiamine test if you have symptoms that could be related to low thiamine, especially when there is a reason your intake or absorption might be reduced. Examples include persistent nausea or poor intake, unexplained fatigue or weakness, numbness or tingling in your hands or feet, balance problems, or memory and concentration changes.
Testing is also commonly considered when your risk is higher even if symptoms are mild. That includes heavy alcohol use, a history of bariatric or other gastrointestinal surgery, chronic vomiting, malabsorption conditions, long-term diuretic use, dialysis, or a very restricted diet.
If you are already taking thiamine, a blood level can help confirm whether your current dose and routine are getting you into a safer range, or whether you need a different plan. Your clinician may pair this with other nutrition markers because multiple deficiencies can overlap and produce similar symptoms.
This is a laboratory-developed test performed in a CLIA-certified lab using LC–MS/MS; results should be interpreted with your clinician and are not a standalone diagnosis.
Lab testing
Order a Vitamin B1 (thiamine) test through Vitals Vault and get drawn at a nearby Quest location.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
Vitals Vault lets you order a Vitamin B1 (thiamine) plasma/serum test directly, then review your results in one place. If you are trying to connect symptoms to nutrition status, having a clear baseline can help you decide what to do next with your clinician.
After your result posts, you can use PocketMD to ask practical questions like what a low value could mean in your situation, what companion labs to consider, and when a retest is reasonable. That way, you are not left guessing based on a single number.
If your thiamine result suggests a broader pattern, you can also add related labs through Vitals Vault so you can look at nutrient status, blood counts, and metabolic markers together rather than in isolation.
- Order online and visit a local Quest draw site
- Clear, plain-language result context with PocketMD
- Easy retesting to track changes over time
Key benefits of Vitamin B1 (Thiamine) testing
- Helps identify thiamine deficiency risk before symptoms become severe.
- Adds objective data when fatigue, neuropathy symptoms, or brain fog have many possible causes.
- Supports monitoring after bariatric surgery, chronic vomiting, or other malabsorption risks.
- Helps evaluate nutrition status in the setting of heavy alcohol use or poor dietary intake.
- Provides a baseline before and after thiamine supplementation so you can track response.
- Guides whether you should broaden testing to other B vitamins, magnesium, and anemia markers.
- Uses LC–MS/MS for specific measurement with fewer interferences than some older methods.
What is Vitamin B1 (thiamine)?
Vitamin B1 (thiamine) is a water-soluble vitamin your body uses to convert food into energy and to support normal nerve signaling. Inside cells, thiamine is converted into active forms (such as thiamine pyrophosphate) that help key enzymes run the pathways that generate energy from carbohydrates.
Because your body stores only limited amounts of thiamine, low intake or increased losses can lead to deficiency over weeks to months. Deficiency can affect the nervous system, heart, and brain, and it can overlap with other nutrient problems.
A plasma or serum thiamine test measures the amount of thiamine circulating in the liquid portion of your blood. It can be helpful for screening and monitoring, although in some clinical settings clinicians may also use whole-blood thiamine or functional tests (such as transketolase activity) to assess tissue status.
Why method matters (LC–MS/MS)
LC–MS/MS (liquid chromatography–tandem mass spectrometry) separates thiamine from other compounds and detects it by mass, which improves analytical specificity. In plain terms, it helps the lab measure the right molecule more reliably, especially at low concentrations.
Plasma/serum vs whole blood
Thiamine is present in both the liquid portion of blood and inside red blood cells. Plasma/serum levels can shift with recent intake and short-term changes, while whole-blood measures may reflect longer-term status more closely. If your result and your symptoms do not match, your clinician may consider a different specimen type or additional markers.
What do my Vitamin B1 (thiamine) results mean?
Low thiamine levels
A low thiamine result suggests your body may not be getting enough thiamine, not absorbing it well, or losing it faster than usual. This can be seen with poor intake, heavy alcohol use, prolonged vomiting, malabsorption, or after bariatric surgery. Low levels can contribute to fatigue, weakness, neuropathy symptoms, and cognitive changes, but these symptoms are not specific to thiamine alone. Your clinician will usually look for contributing factors and consider checking related nutrients and blood counts.
In-range (optimal) thiamine levels
An in-range result makes clinically significant thiamine deficiency less likely at the time of testing. If you still have symptoms, the next step is often to look for other explanations such as iron deficiency, thyroid issues, diabetes-related neuropathy, B12 deficiency, medication effects, or sleep problems. If you recently started supplements, an in-range value can also indicate that your current routine is restoring levels. Trend matters, so repeating the test may be useful if your risk factors continue.
High thiamine levels
High thiamine in plasma or serum is most often due to recent supplementation, including multivitamins, B-complex products, or high-dose thiamine prescribed for a specific reason. Thiamine is water-soluble, so excess is typically excreted in urine, but very high intake can still make interpretation tricky because the timing of your last dose can raise the measured level. A high result is usually not a sign of toxicity on its own, but it is a reason to review your supplement list and dosing schedule with your clinician. If you are supplementing and still have symptoms, your clinician may look for other causes rather than escalating thiamine automatically.
Factors that influence thiamine results
Recent supplements and the timing of your last dose can raise plasma/serum thiamine, sometimes more than your longer-term tissue status. Alcohol use, malabsorption, chronic diarrhea, and prolonged vomiting can lower levels, while diuretics may increase urinary losses in some people. Severe illness and inflammation can shift nutrient distribution and make a single blood value harder to interpret. Lab reference ranges and specimen type (plasma vs serum vs whole blood) also vary, so it helps to compare your result to the range printed on your report and to your prior results from the same method.
What’s included
- Vitamin B1 (Thiamine), Serum/Plasma, Lc/Ms/Ms
Frequently Asked Questions
Do I need to fast for a thiamine (vitamin B1) blood test?
Fasting is not always required, but it is important to follow the collection instructions on your order. Because recent supplements and meals can affect plasma/serum levels, your clinician may prefer a morning draw and may ask you to avoid taking thiamine-containing supplements until after the blood draw.
What is the difference between thiamine in plasma/serum and whole blood?
Plasma/serum measures thiamine in the liquid portion of your blood and can be more sensitive to recent intake. Whole-blood testing includes thiamine inside red blood cells and may reflect longer-term status more closely. If your clinical picture is complex, your clinician may choose one approach over the other.
What symptoms can low vitamin B1 cause?
Low thiamine can contribute to fatigue, weakness, poor appetite, numbness or tingling, balance problems, and cognitive changes. In more severe cases, it can affect the heart and nervous system. These symptoms overlap with many other conditions, so testing helps clarify whether thiamine is part of the picture.
How long after starting thiamine supplements should I retest?
Retest timing depends on why you are supplementing and how low your baseline was. Many clinicians recheck within about 4 to 12 weeks to confirm improvement, especially if you had symptoms or a high-risk situation like bariatric surgery or prolonged vomiting. If you are monitoring a chronic risk factor, periodic testing may be used to track trends.
Can alcohol use lower thiamine levels?
Yes. Alcohol can reduce intake, impair absorption, and increase the likelihood of overall malnutrition, all of which can contribute to low thiamine. If alcohol use is part of your history, your clinician may also consider checking other nutrients and liver-related labs to understand the broader context.
If my thiamine level is normal, does that rule out deficiency?
A normal plasma/serum thiamine level makes deficiency less likely, but it does not always rule it out in every situation. Recent supplementation, timing of the draw, and differences between blood compartments can affect results. If symptoms and risk factors are strong, your clinician may consider additional testing or a different specimen type.