{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,8]],"date-time":"2025-12-08T22:21:25Z","timestamp":1765232485631,"version":"3.40.4"},"reference-count":13,"publisher":"BMJ","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Reports"],"accepted":{"date-parts":[[2017,7,14]]},"abstract":"<jats:p>Vitamin B<jats:sub>12<\/jats:sub>deficiency is a recognised pathology in several populations, with a particular prevalence in an older adult population. We present two cases whereby vitamin B<jats:sub>12<\/jats:sub>deficiency is the causative factor in marked pancytopaenia. Oval macrocytosis and hypersegmented neutrophils were noted on both peripheral blood samples, which are a characteristic finding in macrocytic anaemia due to B<jats:sub>12<\/jats:sub>deficiency. Distinct underlying pathologies were identified in both cases; food-cobalamin malabsorption and pernicious anaemia. Parenteral vitamin B<jats:sub>12<\/jats:sub>supplementation resulted in a marked reticulocytosis and rapid improvement of haematological indices in both cases. We present this series to serve as a reminder that B<jats:sub>12<\/jats:sub>deficiency can present as life-threatening pancytopaenia.It has has multiple underlying pathologies,defined risk populations and has characteristic blood film findings which can guide investigations, diagnosis and treatment.<\/jats:p>","DOI":"10.1136\/bcr-2016-218508","type":"journal-article","created":{"date-parts":[[2017,8,18]],"date-time":"2017-08-18T10:00:05Z","timestamp":1503050405000},"page":"bcr-2016-218508","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":4,"title":["Hypersegmented neutrophils and oval macrocytes in the setting of B<sub>12<\/sub>deficiency and pancytopaenia"],"prefix":"10.1136","volume":"2017","author":[{"given":"Sean James","family":"Farrelly","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kieran Anthony","family":"O\u2019Connor","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2017,8,17]]},"reference":[{"key":"2025042712312372000_2017.aug17_2.bcr-2016-218508.1","doi-asserted-by":"publisher","DOI":"10.1309\/AJCP50AEEYGREWUZ"},{"key":"2025042712312372000_2017.aug17_2.bcr-2016-218508.2","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMcp1113996"},{"key":"2025042712312372000_2017.aug17_2.bcr-2016-218508.3","doi-asserted-by":"crossref","first-page":"107","DOI":"10.1016\/j.amjmed.2007.11.003","article-title":"A sheep in wolf's clothing","volume":"121","author":"Dalsania","year":"2008","journal-title":"Am J Med"},{"key":"2025042712312372000_2017.aug17_2.bcr-2016-218508.4","unstructured":"Wjl MSB . 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