Editing Megaloblastic anemia (section)

{{More medical citations needed|date=September 2018}}

{{Infobox medical condition (new)
| name            = Megaloblastic anemia
| synonyms        = Megaloblastic anaemia
| image           = Hypersegmented neutrophil.png
| caption         = Peripheral blood smear showing hypersegmented neutrophils, characteristic of megaloblastic anemia.
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| field           = [[Hematology]]
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'''Megaloblastic anemia''' is a type of [[macrocytic anemia]]. An [[anemia]] is a [[red blood cell]] defect that can lead to an undersupply of oxygen.<ref>{{Cite web|title=Anemia. Blood patient information|url=http://www.dgft.nhs.uk/anaemia/&ved=2ahUKEwiS4eaP4LzwAhWL_KQKHbaZD-0QFjAVegQILBAC&usg=AOvVaw3Ga6fW2AkPt9lWEy4ob-B9|access-date=2021-05-09|website=UK [[National Health Service]]}}{{Dead link|date=March 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Megaloblastic anemia results from inhibition of [[DNA replication|DNA synthesis]] during red blood cell production.<ref name="urlMegaloblastic Anemia: Overview - eMedicine Hematology">{{cite web |url=http://emedicine.medscape.com/article/204066-overview |title=Megaloblastic Anemia: Overview - eMedicine Hematology |access-date=2009-02-07}}</ref> When DNA synthesis is impaired, the [[cell cycle]] cannot progress from the G2 growth stage to the mitosis (M) stage. This leads to continuing cell growth without division, which presents as macrocytosis.
Megaloblastic anemia has a rather slow onset, especially when compared to that of other anemias.
The defect in red cell DNA synthesis is most often due to [[hypovitaminosis]], specifically [[vitamin B12 deficiency]] or [[folate deficiency]]. Loss of micronutrients may also be a cause.

Megaloblastic anemia which is not caused due to hypovitaminosis may be caused by [[antimetabolite]]s that poison DNA production directly, such as some chemotherapeutic or antimicrobial agents (for example [[azathioprine]] or [[trimethoprim]]).

The pathological state of megaloblastosis is characterized by many large immature and dysfunctional red blood cells ([[megaloblast]]s) in the bone marrow<ref name="titleMegaloblastic (Pernicious) Anemia - Lucile Packard Childrens Hospital">{{cite web |url=http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/hematology/megalob.html |title=Megaloblastic (Pernicious) Anemia - Lucile Packard Children's Hospital |access-date=2008-03-12 |archive-url=https://web.archive.org/web/20080323065724/http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/hematology/megalob.html |archive-date=2008-03-23 |url-status=dead }}</ref> and also by [[hypersegmented neutrophil]]s (defined as the presence of neutrophils with six or more lobes or the presence of more than 3% of neutrophils with at least five lobes).<ref>{{Cite book|url=https://books.google.com/books?id=rEPUDAAAQBAJ&pg=PA85|title=Dacie and Lewis Practical Haematology E-Book|last1=Bain|first1=Barbara J.|last2=Bates|first2=Imelda|last3=Laffan|first3=Mike A.|date=2016-08-11|publisher=Elsevier Health Sciences|isbn=9780702069253|language=en}}</ref> These hypersegmented [[neutrophil]]s can be detected in the [[peripheral blood]]  (using a diagnostic smear of a blood sample).