{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,27]],"date-time":"2026-10-27T23:35:32Z","timestamp":1793144132295,"version":"4.5.0"},"reference-count":33,"publisher":"SAGE Publications","issue":"4","license":[{"start":{"date-parts":[[2022,4,25]],"date-time":"2022-04-25T00:00:00Z","timestamp":1650844800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["Ann Clin Biochem"],"published-print":{"date-parts":[[2022,7]]},"abstract":"<jats:p>Determination of plasma vitamin B12 (B12) is a frequently requested laboratory analysis, mainly employed to establish B12 deficiency. However, an increased level of B12 is a common unexpected finding that may be related to an increased concentration of one of the B12 binding proteins, haptocorrin or transcobalamin. This paper describes the extensive laboratory evaluation of a patient with an elevated level of plasma B12 with various well-established assays. Initial studies suggested the presence of a macromolecule consisting of haptocorrin bound B12. Specific determinations of the B12-binding proteins revealed normal amounts of haptocorrin but a markedly increase in both total and B12 saturated transcobalamin (holo-TC). The results are in accord with the presence of macro-transcobalamin. These experiments reveal that determination of the nature of the B12-macromolecules is troublesome due to differences in assays applied to measure these proteins. In addition, this publication creates awareness of macro-holo-TC as a cause of an unexplained increased B12 level.<\/jats:p>","DOI":"10.1177\/00045632221087132","type":"journal-article","created":{"date-parts":[[2022,3,30]],"date-time":"2022-03-30T09:43:09Z","timestamp":1648633389000},"page":"302-307","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":9,"title":["\u201cMacro transcobalamin causing raised vitamin B12: Case-based laboratory investigation\""],"prefix":"10.1177","volume":"59","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0551-8066","authenticated-orcid":false,"given":"Sjoerd N.","family":"Duim","sequence":"first","affiliation":[{"name":"Department of Clinical Chemistry and Haematology, Haaglanden Medisch Centrum, Den Haag, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"L. 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