Vitamin B1 (thiamine) is a water-soluble B vitamin needed for converting carbohydrates into energy. It plays a central role in glucose metabolism and is important for the normal function of the nervous system and heart. Unlike fat-soluble vitamins, thiamine is not stored in large amounts by the body, so ongoing dietary intake is necessary to maintain adequate levels.
This test measures thiamine diphosphate (TDP), the biologically active form of B1, in red blood cells. Measuring the active form in red cells gives a more accurate picture of true thiamine status than measuring thiamine in serum alone, since it reflects how much functional B1 is available for metabolic processes.
The group most commonly affected by thiamine deficiency is people with heavy or chronic alcohol use. Alcohol impairs thiamine absorption from the gut, reduces liver storage, and increases urinary excretion. Other at-risk groups include people with very restrictive diets, those who have had bariatric surgery, individuals on prolonged intravenous nutrition, and people with gastrointestinal conditions that reduce nutrient absorption.
Early signs of low thiamine can be non-specific: fatigue, poor concentration, irritability, and tingling in the hands or feet. Severe deficiency can lead to beriberi (a condition affecting the heart and nervous system) or Wernicke's encephalopathy, a serious neurological condition seen most often in the context of alcohol-related deficiency.
A diet high in refined carbohydrates can increase thiamine demand because thiamine is required for carbohydrate metabolism. People eating a diet heavy in processed, refined foods and low in whole grains, legumes, nuts, and meat may have suboptimal levels even without a recognised risk factor.
To measure thiamine diphosphate (the active form of B1) in red blood cells and identify whether thiamine levels are sufficient, low, or deficient.
