Vitamin B1 (Thiamine)
Measures the active form of vitamin B1 (thiamine) in whole blood, to see whether your body has enough of this B vitamin.
AI-verified against cited sources. Awaiting expert reviewAlso called B1, TDP, ThDPLOINC 74444-1
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What it is
Vitamin B1, also called thiamine, helps your cells turn food into energy. Your body stores very little of it, so you need a steady supply from foods such as whole grains, fortified cereals, meat, beans and nuts. This test measures thiamine diphosphate, the active form, in whole blood. Most of the thiamine in blood sits inside red blood cells, which is why whole blood is the preferred sample.
Why it matters
Very low thiamine can affect the nerves, heart and brain. Severe, long-lasting deficiency causes beriberi and a brain condition called Wernicke encephalopathy. The test is most often ordered for people at higher risk, such as those with heavy alcohol use, weight-loss surgery or long-lasting vomiting. There is no widely agreed cutoff for deficiency, so the result is read together with symptoms and risk factors.
If it’s low
A low result means your blood has less active thiamine than the lab usually sees. It can be a sign that intake or absorption is too low, or that your body is using more than usual. Because there is no agreed cutoff, your clinician will read it together with your symptoms and health history.
Common causes
- Heavy or long-term alcohol use
- Weight-loss (bariatric) surgery
- Long-lasting vomiting, such as severe nausea in pregnancy (hyperemesis gravidarum)
- A very limited diet or poor nutrition
- Some illnesses that raise the body's needs or reduce absorption, including HIV
What can help
- Talk with your clinician about the cause and whether a thiamine supplement or other treatment is right for you
- Include thiamine-rich foods such as whole grains, fortified cereals, meat, beans and nuts
- If alcohol use is part of the picture, ask your clinician about support
If it’s high
A high result most often means you took a vitamin B1 or multivitamin supplement shortly before the test. High levels from food alone are not expected, and extra thiamine is mostly passed out in the urine.
Common causes
- Vitamin B1, B-complex or multivitamin supplements taken before the draw
- Thiamine given by a clinician as an injection or through an IV
What can help
- Tell the lab and your clinician about any supplements you took in the hours before the draw
- Ask whether the test should be repeated under the lab's preparation instructions if the result is unexpectedly high
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 70–180 nmol/L. Source: Mayo Clinic Laboratories, ARUP Laboratories, Annals of the New York Academy of Sciences.
- Adults (this one applies)70–180 nmol/L
Sources: Mayo Clinic Laboratories, ARUP Laboratories, Annals of the New York Academy of Sciences
If this applies to you
Vitamin B1 means a little more for some people. Open the one that fits you.
Had weight-loss surgery
Low thiamine (vitamin B1) is an early risk after surgery, especially with ongoing vomiting, fast weight loss or eating very little. Guidelines say suspected low thiamine is treated right away, without waiting for the blood result.
What can affect your result
- Recent vitamin B1 or multivitamin supplements
- Fasting: Mayo Clinic Laboratories asks for a 12-hour fast
- Red blood cell volume, because most thiamine in whole blood is inside red cells
- Light and handling: the sample must be protected from light and frozen
- Method: whole-blood thiamine diphosphate is not the same as plasma thiamine or erythrocyte transketolase activity
- Vitamin B1 or multivitamin supplements taken shortly before the draw can raise the result; Mayo Clinic Laboratories asks patients to skip vitamin supplements for 12 hours before the draw.
- The sample must be protected from light and frozen quickly; delays or light exposure can change the result.
- About 80 percent of thiamine in whole blood sits inside red blood cells, so the red cell count can shift whole-blood values.
- Plasma or serum thiamine is a different test. ARUP does not accept those samples for this assay, and their results cannot be compared with a whole-blood result.
Morning draw after an overnight fast is typical. Reflects recent intake. Thiamine stores in the body are limited (Whitfield 2018), so levels can follow intake closely; no standard timeline is published.
When to talk to a clinician
Get urgent care for new confusion, trouble walking or balance, unusual eye movements, or leg swelling with shortness of breath. This matters most if you drink heavily, had weight-loss surgery or have been vomiting for days. These can have many causes, including serious thiamine deficiency, and should not wait for a lab result.
Questions you could ask
- Do my health history, diet or alcohol use put me at higher risk of low thiamine?
- Could a supplement I took recently explain this result?
- What might be causing my level to be low, and is more testing needed?
- Should we recheck it later, and how will we know if it is improving?
Questions people ask
Does a low vitamin B1 result mean I have beriberi?
Not necessarily. Beriberi is a specific illness that develops after severe, long-lasting deficiency. A low number can be an early warning, but clinicians also look at symptoms, diet and health history.
Why is this test done on whole blood instead of serum?
Most thiamine in blood is inside red blood cells, and the active form is found there. ARUP lists whole blood as the preferred sample for thiamine.
Should I take my vitamins the morning of the test?
Check your lab's preparation instructions. Some labs, such as Mayo Clinic Laboratories, ask people to skip vitamin supplements for 12 hours before the draw because recent doses can raise the result. Ask your clinician before changing anything you take regularly.
Show the science and sources
For clinicians and researchers
Whole-blood thiamine diphosphate (ThDP, also called TDP or thiamine pyrophosphate) is the main form of thiamine in whole blood: ARUP puts it at about 90 percent, and a small study summarized by Whitfield 2018 found about 84 percent, with free thiamine, thiamine monophosphate and thiamine triphosphate making up the rest. The ARUP assay measures ThDP only. Mayo's test ID is TDP and its page does not say which forms it quantifies, but it reports the same interval. Both labs use tandem mass spectrometry (Mayo LC-MS/MS; ARUP HPLC-MS/MS). About 80 percent of whole-blood thiamine is in erythrocytes. Both Mayo Clinic Laboratories and ARUP report 70-180 nmol/L, and total whole-blood thiamine is typically 75-195 nmol/L (Whitfield 2018). No universally accepted deficiency cutoff exists; published studies have used a wide range of cutoffs, and best practice is to report the reference interval of the performing lab. Research papers often normalize ThDP to hematocrit or hemoglobin (nmol/L of red cells) and have used erythrocyte ThDP cutoffs from about 118 to 180 nmol/L RBC. The erythrocyte transketolase activation coefficient is a functional alternative. Some labs print results in ug/L; this file does not convert them because the analyte basis (thiamine vs thiamine diphosphate) is not standardized.
LOINC 74444-1 (primary), 32554-8, 2998-3. Specimen: whole-blood.
Sources
- Thiamin (Vitamin B1), WB - Test ID TDP (Mayo Clinic Laboratories Extended Catalog), Mayo Clinic Laboratories
- Vitamin B1 (Thiamine), Whole Blood (test 0080388), ARUP Laboratories
- Thiamine deficiency disorders: diagnosis, prevalence, and a roadmap for global control programs, Annals of the New York Academy of Sciences (2018)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.