Abstract
Vitamin B1 (thiamine) is an essential nutrient that acts as a cofactor for a number of metabolic processes, particularly in energy metabolism. Symptoms of classic thiamine deficiency are recognized as beriberi, although clinical symptoms are nonspecific and recognition of subclinical deficiency is difficult. Therefore, reliable biomarkers of thiamine status are required. Thiamine diphosphate is a cofactor for transketolase, including erythrocyte transketolase (ETK). The ETK activity assay as an indirect, functional marker of thiamine status has been used for over 50 years. The ETK activity assay provides a sensitive and specific biomarker of thiamine status; however, there is a lack of consensus over the cutoffs for deficiency, partly due to a lack of assay harmonization. Here, we provide a step‐by‐step protocol for the measurement of ETK activity and the calculation of the ETK activity coefficient, including detailed explanations of equipment and chemicals required and guidance for quality control procedures. Harmonization of the protocol will provide the basis for the development of internationally recognized cutoffs for thiamine insufficiency. The establishment of quality control materials and a quality assurance scheme are recommended to provide reliability. This will ensure that the ETK activity assay remains an important method for the assessment of thiamine status.
Highlights
A recent study of children and adults found that while both basal and erythrocyte transketolase activity coefficient (ETKAC) correlated with erythrocyte thiamine diphosphate (ThDP), the correlation was stronger for basal activity.[19]
Perceived limitations of the assay include relatively poor precision, lack of standardization, instability of the transketolase enzyme, and lack of consensus about cutoffs for deficiency.[42]. These limitations apply to other assays of thiamine status, such as whole blood ThDP
ETKAC provides a potentially better marker of long-term thiamine status that is less affected than ThDP by acute changes in thiamine intake.[43]
Summary
Thiamine (vitamin B1) is an essential micronutrient. In humans, the majority of thiamine exists in phosphorylated forms: thiamine monophosphate, thiamine diphosphate (ThDP) ( known as thiamine pyrophosphate), and thiamine triphosphate. The use of basal ETK activity rather than ETKAC has been recommended, for the assessment of thiamine status in infants due to potential low levels of apoenzyme caused by long-term low exposure to thiamine.[18] A recent study of children and adults found that while both basal and ETKAC correlated with erythrocyte ThDP, the correlation was stronger for basal activity.[19] Basal (or activated ETK) activity needs to be expressed per mass unit of hemoglobin, and it is necessary to measure the hemoglobin concentration in the same lysate as used for the ETK activity assay. Whole blood samples from 15 participants kept at 4 °C were observed to be stable for 24 h, with no significant change in the ETKAC observed in LH-treated whole blood
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