What causes the excess of immature RBCs in pernicious anemia?

In pernicious anemia, the primary issue leading to the excess of immature red blood cells (RBCs) is the inability to absorb vitamin B12. This vitamin is crucial for proper red blood cell production and maturation. When B12 absorption is hindered, which can occur due to a lack of intrinsic factor—a protein necessary for B12 absorption in the intestines—the body cannot produce mature RBCs effectively.

As a result, the bone marrow attempts to produce more RBCs, leading to an increase in immature cells, known as megaloblasts. These cells are larger and less effective at carrying oxygen compared to fully mature RBCs. The lack of adequate B12 ultimately disrupts the normal maturation process, causing an accumulation of these immature cells in the bloodstream.

Other factors such as an inability to absorb folic acid, excessive blood loss, or infections do not directly relate to the mechanism of pernicious anemia and do not primarily cause the characteristic increase in immature RBCs associated with this condition.