Vitamin B1 (Thiamine) Blood Test (LC‑MS/MS) Biomarker Testing
It measures thiamine status in blood to help evaluate deficiency risk and guide follow-up; order through Vitals Vault with Quest collection and PocketMD.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
This test measures vitamin B1 (thiamine) in your blood using LC‑MS/MS, a highly specific lab method. Thiamine is a water‑soluble vitamin your body needs to turn food into energy and to support nerve and heart function.
Because thiamine stores can run low faster than many other nutrients, a low result can show up when intake is limited, absorption is impaired, or needs are higher than usual. Testing can help you and your clinician decide whether symptoms or risk factors fit with thiamine deficiency and what to do next.
Your result is most useful when it is interpreted alongside your diet, medications, alcohol intake, and other labs that affect nutrition and metabolism.
Do I need a Vitamin B1 (Thiamine) blood test?
You may want a thiamine blood test if you have symptoms that could fit with low thiamine, especially when there is a clear risk factor. People often consider testing when they have persistent fatigue, poor appetite, unexplained weight loss, numbness or tingling in the hands or feet, trouble with balance, or brain fog that does not have an obvious cause.
Testing is also commonly used when your risk is higher even if symptoms are subtle. That includes heavy or long‑term alcohol use, a history of bariatric surgery or other gastrointestinal conditions that affect absorption, prolonged vomiting, very restrictive diets, or periods of high metabolic demand (for example, severe illness). Some medications and medical conditions can also increase the chance of deficiency.
If you are already taking thiamine, a blood level can help confirm whether your status is improving and whether your plan is working. This test supports clinician‑directed care and is not, by itself, a diagnosis of any single condition.
This is a laboratory-developed test performed in a CLIA-certified lab; results should be interpreted with your clinician in the context of symptoms and other labs.
Lab testing
Order a Vitamin B1 (Thiamine) blood test
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) Blood test without waiting for a referral, and you can complete your blood draw at a nearby Quest location. Once your results are back, you can review them in one place and keep them available for future comparisons.
If you are not sure how to interpret a low, in-range, or high thiamine result, PocketMD can help you turn the number into next steps to discuss with your clinician. That usually means checking for common causes of low thiamine, deciding whether companion labs would add clarity, and choosing a reasonable retest window.
This approach works well if you are troubleshooting symptoms, monitoring recovery after a nutrition change, or building a broader lab map when more than one nutrient could be involved.
- Convenient Quest draw locations
- Clear, shareable results for your clinician
- PocketMD guidance for follow-up and retesting
Key benefits of Vitamin B1 (Thiamine) testing
- Helps identify thiamine deficiency risk before symptoms become severe.
- Adds objective context when fatigue, neuropathy symptoms, or cognitive changes are unexplained.
- Supports evaluation of malabsorption risk after bariatric surgery or chronic GI issues.
- Helps monitor whether thiamine repletion is working when you change diet or treatment.
- Can clarify nutrition status in people with heavy alcohol use or poor intake.
- Pairs well with other nutrition and anemia labs to find multi-nutrient patterns.
- Creates a baseline you can trend over time in your Vitals Vault record.
What is Vitamin B1 (thiamine)?
Vitamin B1 (thiamine) is a water‑soluble vitamin that your cells use to convert carbohydrates into usable energy. In its active form (thiamine pyrophosphate), it supports enzymes that help run core metabolic pathways, which is why low thiamine can affect high‑energy tissues such as the brain, nerves, and heart.
Unlike some vitamins that can be stored for long periods, thiamine reserves can be limited. If intake drops, absorption is reduced, or needs rise, your level can fall relatively quickly. That is one reason clinicians take thiamine status seriously in settings like prolonged vomiting, malnutrition, or heavy alcohol use.
A “Vitamin B1 (Thiamine) Blood LC‑MS/MS” test measures thiamine in blood using liquid chromatography–tandem mass spectrometry. LC‑MS/MS is valued for specificity, which helps reduce interference compared with less specific methods.
Your clinician may still consider other markers and your clinical picture, because symptoms can overlap with other nutrient deficiencies (such as vitamin B12) and with non-nutritional causes.
What do my Vitamin B1 (Thiamine) results mean?
Low thiamine levels
A low thiamine result suggests your body may not have enough vitamin B1 to meet metabolic needs. Common reasons include low intake, impaired absorption (for example after bariatric surgery), prolonged vomiting, or heavy alcohol use. Because symptoms can be nonspecific, your clinician may look for patterns with other labs (such as magnesium, folate, vitamin B12, CBC, and metabolic markers) and review your diet and medications. If you have neurologic symptoms, confusion, or trouble walking, low thiamine can be clinically urgent and should be addressed promptly.
In-range (optimal) thiamine levels
An in-range result generally means your current thiamine status is adequate at the time of testing. If you still have symptoms, this can help narrow the search toward other causes, including other nutrient issues, thyroid problems, anemia, blood sugar dysregulation, sleep problems, or medication effects. In-range does not always rule out functional issues in every situation, so your clinician may still consider your overall risk factors and whether additional testing is appropriate. Trending over time can be helpful if you recently changed diet or started supplementation.
High thiamine levels
A high thiamine level is most often explained by recent supplementation or high intake from fortified foods. Thiamine is water‑soluble, so excess is typically excreted in urine, and high blood levels are not usually a sign of toxicity by themselves. However, a result that is unexpectedly high without supplements may prompt a review of lab timing, dosing, and whether the specimen type matches the reference interval used by the lab. Your clinician may also consider whether the result aligns with your symptoms and other nutrition markers.
Factors that influence thiamine results
Supplement timing is one of the biggest drivers of variation, so tell your clinician if you took thiamine or a B‑complex shortly before the draw. Alcohol use, malabsorption conditions, bariatric surgery, prolonged poor intake, and repeated vomiting can all lower thiamine status. Severe illness and high carbohydrate loads can increase thiamine demand, which may contribute to deficiency in susceptible people. Pre-analytical handling and the specific lab method can also affect results, so it is best to compare trends using the same lab when possible.
What’s included
- Vitamin B1 (Thiamine), Blood, Lc/Ms/Ms
Frequently Asked Questions
Do I need to fast for a Vitamin B1 (thiamine) blood test?
Fasting is not always required, but it is important to be consistent if you are trending results. If you take thiamine or a B‑complex, ask your clinician whether to hold it before the draw, because recent dosing can raise the measured level.
How is thiamine deficiency tested—blood thiamine vs other tests?
This test measures thiamine in blood using LC‑MS/MS. Some clinicians may also use functional markers (such as enzyme activity tests) or evaluate related findings like anemia patterns, magnesium status, and overall nutrition labs. The best choice depends on your symptoms, risk factors, and what your lab offers.
What symptoms can low thiamine cause?
Low thiamine can contribute to fatigue, irritability, poor appetite, numbness or tingling, muscle weakness, balance problems, and cognitive changes. In severe cases, it can affect the heart and nervous system. Because these symptoms overlap with many conditions, testing helps confirm whether thiamine status is part of the picture.
How soon after starting thiamine should I retest?
Retest timing depends on why you were low and how aggressive the repletion plan is. Many people recheck in about 4–8 weeks to confirm improvement, while higher-risk situations (such as post-bariatric surgery complications or significant symptoms) may warrant earlier follow-up guided by a clinician.
Can alcohol use affect thiamine levels?
Yes. Alcohol can reduce intake, impair absorption, and interfere with how thiamine is used in the body. If alcohol use is part of your history, a thiamine test can be a practical way to assess risk and guide a safer nutrition plan.
What other labs are commonly checked with thiamine?
Thiamine is often interpreted alongside other nutrition and metabolic labs, such as CBC, CMP, magnesium, vitamin B12, folate, iron studies, and sometimes vitamin D. Your clinician may choose companion tests based on your symptoms and the most likely causes of deficiency.