Vitamin B1 (thiamine) test: what the result means

Thiamine (vitamin B1) is a water-soluble vitamin that cells need in order to produce energy, and that the nervous system and the muscles need in order to work properly. The body does not store B1 in large amounts, so its stores depend on a steady intake from food — grains, meat, legumes. A blood test to establish the amount of B1 is done rarely, and mostly when there is a suspicion that a person is not getting enough of one or several B group vitamins. The clearest and best-described consequence of B1 deficiency is beriberi, which can present in two forms: “wet” beriberi, which affects the heart and blood vessels, or “dry” beriberi and Wernicke–Korsakoff syndrome, which affect the nervous system. The highest risk is in people who misuse alcohol, improperly fed infants, patients on dialysis, and people with certain genetic features. Because B1 is water-soluble, an excess of it rarely builds up in the body — usually the surplus amount is simply passed out in the urine.

• When there are symptoms suggesting a possible shortage of B group vitamins (B1 among them) — weakness, tiredness, changes in mood
• When beriberi is suspected — in the case of disorders of the nervous system or of the heart and blood vessels
• In people who misuse alcohol over a long period — because of the increased risk of B1 deficiency
• In patients on dialysis, or after operations on the digestive tract that can interfere with the uptake of vitamins
• When coeliac disease, Crohn's disease or another malabsorption syndrome that interferes with the uptake of vitamins is suspected

• Before a B group vitamin blood test you may need to avoid food and drink for a few hours — talk to your doctor or the laboratory about the specific requirements
• Tell your doctor about any vitamin preparations and food supplements you take — they can affect the result

General points that apply to any blood sample are gathered here: how to prepare for a blood test.

Reference range

This page does not give a numeric reference range for vitamin B1 in blood. An exact, widely recognised numeric interval for blood thiamine (B1) could not be reliably confirmed in the MedlinePlus sources we use (Beriberi; Vitamin B Test) — they mention the test itself, but do not state specific values or units. Until a reliable source with a specific interval is found, the exact interval used by your laboratory is the one to go by; you will find it on your own result sheet. See also how to read blood test results.

Vitamin B1 is water-soluble — the body does not store it, so a surplus is usually passed out in the urine, and a raised blood level occurs extremely rarely. Per MedlinePlus, large amounts of B group vitamins in the body are sometimes linked to liver disease or to other health problems, rather than to an excess of B1 itself.

Causes listed for a high result:

• Food supplements or injections taken in larger amounts than needed
• Liver disease or other health problems that can raise the total amount of B group vitamins (MedlinePlus)

What is usually looked at after a high result:

• Which food supplements are being taken and at what doses — to be discussed with your doctor
• Liver function markers, if the rise is not related to supplements

A low vitamin B1 result (deficiency)

A lowered amount of vitamin B1 (thiamine) is linked to beriberi: “wet” beriberi affects the heart and blood vessels, while “dry” beriberi and Wernicke–Korsakoff syndrome affect the nervous system. The highest risk is in people who misuse alcohol, improperly fed infants and patients on dialysis.

Causes listed for a low result:

• Long-term alcohol use
• Improper infant feeding
• Dialysis
• Genetic factors
• Diseases of the digestive tract or operations on it that interfere with the uptake of vitamins (for example coeliac disease)

Symptoms listed for a shortage of vitamin B1:

• Dry beriberi: difficulty walking, loss of feeling in the hands and feet, muscle paralysis, confusion, pain, speech difficulties, problems with eye movements, tingling, vomiting
• Wet beriberi: waking at night short of breath, a faster heart rate, breathlessness during physical exertion, swelling of the lower legs

What is usually looked at after a low result:

• Whether there is a shortage of other B group vitamins (for example B12, folic acid) — these are often assessed together
• Alcohol drinking habits and diet
• Conditions of the digestive tract that could interfere with uptake
• An assessment of the nervous system and of how the heart is working, if symptoms have already appeared