{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,18]],"date-time":"2026-06-18T09:54:01Z","timestamp":1781776441604,"version":"3.54.5"},"reference-count":18,"publisher":"BMJ","issue":"7","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["J Clin Pathol"],"accepted":{"date-parts":[[2026,4,18]]},"published-print":{"date-parts":[[2026,7]]},"abstract":"<jats:p>Transitioning from total to active vitamin B12 testing may influence diagnostic categorisation and costs. In this retrospective population study, a total of 181 794 vitamin B12 results from primary care requests in a UK laboratory were analysed -90 036 using total B12 assay before transitioning, and 91 758 using active B12 assay after transitioning- according to the National Institute for Health and Care Excellence (NICE)-defined thresholds. Compared with total B12, active B12 testing identified proportionately fewer patients as deficient (2.1% vs 6.5%) or indeterminate (37.0% vs 46.2%), and more as deficiency-unlikely (60.9% vs 47.3%). Although active B12 improved classification and may reduce the need for confirmatory testing by classifying fewer individuals as indeterminate, it incurred substantially higher cost, with an estimated 26-fold increase in expenditure to identify one deficient patient based on unit test cost in the NICE guidance. While active B12 may enhance diagnostic precision, its financial impact could limit broader adoption for routine testing unless test costs decrease.<\/jats:p>","DOI":"10.1136\/jcp-2025-210520","type":"journal-article","created":{"date-parts":[[2026,5,11]],"date-time":"2026-05-11T17:20:28Z","timestamp":1778520028000},"page":"494-497","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Population-level evaluation of diagnostic categorisation and cost implications on transitioning from total vitamin B12 to active B12 assay"],"prefix":"10.1136","volume":"79","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0468-5679","authenticated-orcid":false,"given":"Amro","family":"Maarouf","sequence":"first","affiliation":[{"name":"Blood Sciences, Black Country Pathology Services, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, England, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rachel L","family":"Griffiths","sequence":"additional","affiliation":[{"name":"Blood Sciences, Black Country Pathology Services, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, England, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jayne","family":"Parkes","sequence":"additional","affiliation":[{"name":"Blood Sciences, Black Country Pathology Services, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, England, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7483-9253","authenticated-orcid":false,"given":"Rousseau Mariano","family":"Gama","sequence":"additional","affiliation":[{"name":"Blood Sciences, Black Country Pathology Services, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, England, UK"},{"name":"School of Medicine and Clinical Practice, University of Wolverhampton, Wolverhampton, England, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1306-8832","authenticated-orcid":false,"given":"Tejas","family":"Kalaria","sequence":"additional","affiliation":[{"name":"Blood Sciences, Black Country Pathology Services, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, England, UK"},{"name":"School of Medicine and Clinical Practice, University of Wolverhampton, Wolverhampton, England, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,5,11]]},"reference":[{"key":"2026061802100684000_79.7.494.1","doi-asserted-by":"crossref","first-page":"17040","DOI":"10.1038\/nrdp.2017.40","article-title":"Vitamin B12 deficiency","volume":"3","author":"Green","year":"2017","journal-title":"Nat Rev Dis Primers"},{"key":"2026061802100684000_79.7.494.2","doi-asserted-by":"crossref","DOI":"10.1136\/bmj.g5226","article-title":"Vitamin B12 deficiency","volume":"349","author":"Hunt","year":"2014","journal-title":"BMJ"},{"key":"2026061802100684000_79.7.494.3","doi-asserted-by":"crossref","DOI":"10.3390\/ijms25158021","article-title":"Vitamin B12 Metabolism: A Network of Multi-Protein Mediated Processes","volume":"25","author":"Mucha","year":"2024","journal-title":"Int J Mol Sci"},{"key":"2026061802100684000_79.7.494.4","doi-asserted-by":"publisher","DOI":"10.1080\/10408363.2021.1885339"},{"key":"2026061802100684000_79.7.494.5","unstructured":"NICE guideline NG239 NI . 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