Vitamin B1 (thiamine)

Most UK labs measure thiamine diphosphate in whole blood, with ranges such as 66 to 200 nmol/L, but some report a red cell value per gram of haemoglobin or an older enzyme activation test, each with its own range.

Thiamine, vitamin B1, is a water-soluble vitamin the body needs to turn carbohydrate into energy and to keep nerves and the heart working. The body stores only a few weeks' worth, so it runs short quickly when intake is poor or absorption fails. The UK test measures its active form, thiamine diphosphate, inside red blood cells.

It is requested in people who drink heavily, after weight-loss surgery, in prolonged vomiting including severe pregnancy sickness, in eating disorders and refeeding, in people on long-term intravenous feeding or dialysis, and when unexplained confusion, nerve problems or heart failure are being looked into.

• Thiamine supplements and B-vitamin injections
• Fortified foods and energy drinks, slightly

• Heavy alcohol use, which both reduces intake and blocks absorption
• Prolonged vomiting, including severe pregnancy sickness
• Weight-loss surgery and other causes of poor absorption
• Eating disorders, very restricted diets and refeeding after starvation
• Diuretic (water) tablets over the long term, and dialysis
• Heart failure, older age and long-term illness, in the general population

• A recent supplement or B-vitamin injection raises it within hours, so the test is best done before treatment starts
• The sample must be protected from light and processed promptly
• Different methods (whole blood, red cell, enzyme activation) give different numbers that are not comparable

An EDTA whole blood sample protected from light, ideally taken before any thiamine is given. In an unwell person doctors usually give thiamine first and do not wait for the result.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.