Mechanism and Classification of Anemia in Vitamin B12 Deficiency

Pathophysiological Mechanism

• Vitamin B12 deficiency leads to impaired DNA synthesis, causing maturation arrest and ineffective erythropoiesis due to apoptosis of rapidly dividing erythroblasts, resulting in macrocytic anemia 1, 2
• The defective DNA synthesis leads to maturation arrest and ineffective early erythropoiesis 1
• Erythroblasts undergoing rapid division during erythropoiesis succumb to apoptosis (programmed cell death) 2
• This results in fewer cells completing maturation into functional red blood cells 2

Absorption and Causes of Deficiency

• Decreased hydrochloric acid production and reduced availability of intrinsic factor can lead to vitamin B12 deficiency 3, 4

Classification of Anemia

• Vitamin B12 deficiency anemia is classified as a macrocytic anemia 5, 6, 7
• Characteristics include a mean corpuscular volume (MCV) > 100 fL 6, 7
• Megaloblastic features due to impaired DNA synthesis are present 5, 6
• Low reticulocyte index (RI) indicates decreased red blood cell production 6
• Abnormally large erythrocyte precursors in the bone marrow are characteristic of megaloblastic macrocytic anemia 6