Anemia is defined as the reduced O2 carrying capacity of blood that occurs mainly due to reduced total RBCs.

What is Ischemia?

Ischemia is defined as the reduction in blood supply to a tissue or organ. The main purpose of the blood is the transportation of nutrients across the cells. If the cells don’t receive the nutrients, their metabolism comes to a halt, hence resulting in their death. If left uncared, mass death of cells and tissues occurs. This difference between anemia and ischemia is to be noted which is of main importance.

Damage of brain tissue due to ischemia

Classification of Anemia – Based on Etiology

  1. Anemia due to increased RBC destruction
  2. Anemia due to decreased RBC production
  3. Anemia due to blood loss

Anemia due to blood loss

It is the reduction in blood supply due to intravascular blood loss. This is an acute condition because the rate of loss is less than the rate of regeneration. Since there is a reduction in blood supply, there is a need for more production of RBCs to carry more oxygen.

The loss of blood is temporarily compensated by water leading to  Hemodilution and reduction of hemostasis (occurs also due to hemodilution and pre-existing continuous blood loss leading to a decrease in platelet and coagulation cascade). Since the cells don’t receive proper oxygen, hypoxia occurs. As an attempt to prevent the conversion of hypoxia to anoxia, the erythropoietin levels increase which stimulates the production of RBCs.

Iron is required for the production of RBCs, if the blood loss occurs internally, the iron is recaptured and reused. This doesn’t occur if the blood loss is external. In some cases where the blood loss is severe, the iron ions cannot be substituted at a large rate and this can lead to a deficiency of iron. This is referred to as iron deficiency anemia.

This condition is chronic and occurs in extreme traumatic cases. If the blood loss is more than 20% of total volume then hypovolemic shock occurs ultimately leading to death.

Hemolytic Anemia


Anemia can also occur due to the destruction of RBCs. This is known as hemolytic anemia. Age is a major cause of this condition. There are two types, extravascular and intravascular. The following table shows their differences.

Intravascular Extravascular 
Occurs in the vessel wallOccurs in spleen
Occurs due to trauma of valves, fixation by complementDue to a decrease in deformability inside the splenic capsule
Can occur in diseases like jaundice, hemoglobinemiaCan occur in splenomegaly and jaundice
Large amounts of Hb is releasedPhagocytosis of Hb by macrophages
Intravascular and extravascular hemolysis

In intravascular, the Hb gets converted to Meth-Hb (methylated version), the kidney when excrete’s Meth-Hb, it forms a reddish-brown color in urine. Iron deficiency may also accompany in some cases. An increase in bilirubin occurs, resulting in gall stone formation. 

Increased plasma iron load and its renal handling causes renal haemosiderosis. In chronic cases of blood loss, extramedullary haematopoiesis occurs. Peripheral blood picture shows prominent reticulocytes and a decrease in serum-free haptoglobin levels.

Increased free Hb in the blood binds to serum haptoglobin and thus decreases its levels.

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