Macrocytic Anaemia and Its Causes

Vitamin B12 and Absorption

• In cyanocobalamin, the reactive center of the vitamin B12 molecule is attached to a cyanide group.
• Vitamin B12 is mainly combined with intrinsic factor (IF) in the stomach for absorption.
• The cubilin receptor directs the endocytosis of the cubilin-IF-B12 complex into the ileal cell for absorption.

Vitamin B12 Release and Absorption

• Gastric acid and pepsin release dietary B12 from food for binding to intrinsic factor (IF) in the stomach.
• The maximum amount of B12 that can be absorbed from a single oral dose via the IF-cubam mechanism is 1.5-2.0 μg.

Megaloblastic Anemias

• The characteristic abnormality seen in the bone marrow erythroblasts in megaloblastic anemias is asynchronous maturation of the nucleus.
• Vitamin B12 deficiency is most commonly associated with defective DNA synthesis, causing megaloblastic anemias.
• Apart from vitamin deficiencies, other conditions like inherited disorders of DNA synthesis may cause an identical hematological appearance to megaloblastic anemias.

Vitamin B12 Transport

• The main plasma-binding protein responsible for delivering Vitamin B12 to the bone marrow and other tissues is transcobalamin (TC).
• Vitamin B12 becomes attached to the plasma-binding protein transcobalamin (TC) in the ileal cells.

Macrocytic Anemia

• In macrocytic anemia, an elevated MCV may be reported as an artefact by an automated cell counter due to the presence of cytoplasmic fragments or Howell-Jolly bodies.

Learn about the causes of macrocytic anaemia and the different types, including megaloblastic and non-megaloblastic anaemias. Understand the factors that can result in an elevated mean corpuscular volume (MCV) and how it may be an artefact reported by an automated cell counter.