Anemia types and classification

Anemia is the blood disorder, characterized by the reduction in:

1. Red blood cell (RBC) count

2. Hemoglobin content

3. Packed cell volume (PVC).

Generally, reduction in RBC count, hemoglobin content and PCV occurs because of:

1. Decreased production of RBC

2. Increased destruction of RBC

3. Excess loss of blood from the body.

All these incidents are caused either by inherited disorders or environmental influences such as nutritional

problem, infection and exposure to drugs or toxins.


Anemia is classified by two methods:

1. Morphological classification

2. Etiological classification.


Morphological classification depends upon the size and color of RBC. Size of RBC is determined by mean corpuscular volume (MCV). Color is determined by mean corpuscular hemoglobin concentration (MCHC). By this method, the anemia is classified into four types:

1. Normocytic Normochromic Anemia

Size (MCV) and color (MCHC) of RBCs are normal. But the number of RBC is less.

2. Macrocytic Normochromic Anemia

RBCs are larger in size with normal color. RBC count is less.

3. Macrocytic Hypochromic Anemia

RBCs are larger in size. MCHC is less, so the cells are pale (less colored).

4. Microcytic Hypochromic Anemia

RBCs are smaller in size with less color.


On the basis of etiology (study of cause or origin), anemia is divided into five types :

1. Hemorrhagic anemia

2. Hemolytic anemia

3. Nutrition deficiency anemia

4. Aplastic anemia

5. Anemia of chronic diseases.

1. Hemorrhagic Anemia

Hemorrhage refers to excessive loss of blood. Anemia due to hemorrhage is known as hemorrhagic

anemia. It occurs both in acute and chronic hemorrhagic conditions.

Acute hemorrhage

Acute hemorrhage refers to sudden loss of a large quantity of blood as in the case of accident. Within about 24 hours after the hemorrhage, the plasma portion of blood is replaced. However, the replacement of RBCs does not occur quickly and it takes at least 4 to 6 weeks. So with less number of RBCs, hemodilution occurs. However, morphologically the RBCs are normocytic and normochromic. Decreased RBC count causes hypoxia, which stimulates the bone marrow to produce more number of RBCs. So, the condition is corrected within 4 to 6 weeks.

Chronic hemorrhage

It refers to loss of blood by internal or external bleeding, over a long period of time. It occurs in conditions like peptic ulcer, purpura, hemophilia and menorrhagia. Due to continuous loss of blood, lot of iron is lost

from the body causing iron deficiency. This affects the synthesis of hemoglobin resulting in less hemoglobin content in the cells. The cells also become small. Hence, the RBCs are microcytic and hypochromic.

2. Hemolytic Anemia

Hemolysis means destruction of RBCs. Anemia due to excessive hemolysis which is not compensated by

increased RBC production is called hemolytic anemia. It is classified into two types:

A. Extrinsic hemolytic anemia.

B. Intrinsic hemolytic anemia.

A. Extrinsic hemolytic anemia: It is the type of anemia caused by destruction of RBCs by external factors.

Healthy RBCs are hemolized by factors outside the blood cells such as antibodies, chemicals and drugs.

Extrinsic hemolytic anemia is also called autoimmune hemolytic anemia.

Common causes of external hemolytic anemia:

i. Liver failure

ii. Renal disorderiii. Hypersplenism

iv. Burns

v. Infections like hepatitis, malaria and septicemia

vi. Drugs such as penicillin, antimalarial drugs and sulfa drugs

vii. Poisoning by chemical substances like lead, coal and tar

viii. Presence of isoagglutinins like antiRh

ix. Autoimmune diseases such as rheumatoid arthritis and ulcerative colitis.

B. Intrinsic hemolytic anemia: It is the type of anemia caused by destruction of RBCs because of the defective RBCs. There is production of unhealthy RBCs, which are short lived and are destroyed soon. Intrinsic hemolytic anemia is often inherited and it includes sickle cell anemia and thalassemia.

Because of the abnormal shape in sickle cell anemia and thalassemia, the RBCs become more fragile and susceptible for hemolysis.

Sickle cell anemia

Sickle cell anemia is an inherited blood disorder, characterized by sickleshaped red blood cells. It is also called hemoglobin SS disease or sickle cell disease. It is common in people of African origin.

Sickle cell anemia is due to the abnormal hemoglobin called hemoglobin S (sickle cell hemoglobin). In this, αchains are normal and βchains are abnormal. The molecules of hemoglobin S polymerize into long chains and precipitate inside the cells. Because of this, the RBCs attain sickle (crescent) shape and become more fragile leading to hemolysis. Sickle cell anemia occurs when a person inherits two abnormal genes (one from each parent). In children, hemolyzed sickle cells aggregate and block the blood vessels, leading to infarction (stoppage of blood supply). The infarction is common in small bones.

The infarcted small bones in hand and foot results in varying length in the digits. This condition is known as hand and foot syndrome. Jaundice also occurs in these children.


Thalassemia is an inherited disorder, characterized by abnormal hemoglobin. It is also known as Cooley’s nemia or Mediterranean anemia. It is more common in Thailand and to some extent in Mediterranean countries.

Thalassemia is of two types:

i. αthalassemia

ii. βthalassemia.

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