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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\u2010by\u2010step 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.<\/jats:p>","DOI":"10.1111\/nyas.14547","type":"journal-article","created":{"date-parts":[[2020,12,24]],"date-time":"2020-12-24T04:08:32Z","timestamp":1608782912000},"page":"77-84","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":57,"title":["Erythrocyte transketolase activity coefficient (ETKAC) assay protocol for the assessment of thiamine status"],"prefix":"10.1111","volume":"1498","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7380-9797","authenticated-orcid":false,"given":"Kerry S.","family":"Jones","sequence":"first","affiliation":[{"name":"NIHR BRC Nutritional Biomarker Laboratory, MRC Epidemiology Unit University of Cambridge Cambridge UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Damon A.","family":"Parkington","sequence":"additional","affiliation":[{"name":"NIHR BRC Nutritional Biomarker Laboratory, MRC Epidemiology Unit University of Cambridge Cambridge UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lorna J.","family":"Cox","sequence":"additional","affiliation":[{"name":"NIHR BRC Nutritional Biomarker Laboratory, MRC Epidemiology Unit University of Cambridge Cambridge UK"},{"name":"MRC Elsie Widdowson Laboratory Cambridge UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9998-051X","authenticated-orcid":false,"given":"Albert","family":"Koulman","sequence":"additional","affiliation":[{"name":"NIHR BRC Nutritional Biomarker Laboratory, MRC Epidemiology Unit University of Cambridge Cambridge UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2020,12,22]]},"reference":[{"key":"e_1_2_13_2_1","doi-asserted-by":"publisher","DOI":"10.1177\/0148607114565245"},{"key":"e_1_2_13_3_1","doi-asserted-by":"publisher","DOI":"10.1111\/nyas.13919"},{"key":"e_1_2_13_4_1","doi-asserted-by":"publisher","DOI":"10.3389\/fnut.2016.00016"},{"key":"e_1_2_13_5_1","doi-asserted-by":"publisher","DOI":"10.3390\/nu9070676"},{"key":"e_1_2_13_6_1","doi-asserted-by":"crossref","DOI":"10.1093\/oso\/9780195171693.001.0001","volume-title":"Principles of Nutritional Assessment","author":"Gibson R.S.","year":"2005"},{"key":"e_1_2_13_7_1","doi-asserted-by":"publisher","DOI":"10.1515\/cclm-2017-0054"},{"key":"e_1_2_13_8_1","doi-asserted-by":"publisher","DOI":"10.1093\/jn\/78.2.179"},{"key":"e_1_2_13_9_1","doi-asserted-by":"publisher","DOI":"10.1016\/0009-8981(71)90496-7"},{"key":"e_1_2_13_10_1","doi-asserted-by":"publisher","DOI":"10.1177\/000456328702400106"},{"key":"e_1_2_13_11_1","first-page":"126","article-title":"Clinical chemical methods for the routine assessment of the vitamin status in human populations. 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