KEY POINTS

• Vitamin B12 and folate deficiencies are the most important causes of megaloblastic anemia.
• The main cause of vitamin B12 deficiency that results in megaloblastic anemia is pernicious anemia caused by autoimmune destruction of gastric parietal cells.
• The prevalence of folate deficiency has decreased because of widespread food folate fortification, but it still occurs among the poor, elderly, and alcoholics, particularly in countries that do not fortify the diet. It can also result from malabsorption or increased cell turnover and increased demand.
• Nuclear-cytoplasmic asynchrony from the ineffective DNA synthesis causes megaloblastic changes in the bone marrow with resulting anemia and cytopenias.

Med Clin N Am 101 (2017) 297–317
https://dx.doi.org/10.1016/j.mcna.2016.09.013