Anemia Classification

Anemia

Decrease in hemoglobin concentration according to age, sex, built and location is called Anemia. Anemia is the most common disorder of the blood. The several kinds of anemia are produced by a variety of underlying causes. It can be classified in a variety of ways including etiology of disease and based on the morphology of RBCs.

Classification of Anemia

Morphological Approach

Red blood cell size:

In the morphological approach, anemia is classified by the size of red blood cells; this is either done automatically or on microscopic examination of a peripheral blood smear. The size is reflected in the mean cell volume (MCV).

If the cells are smaller than normal (under 80 fl), the anemia is said to be microcytic if they are normal size (80–101 fl), normocytic and if they are larger than normal (over 101 fl), the anemia is classified as macrocytic.

This scheme quickly exposes some of the most common causes of anemia for example, a microcytic anemia is often the result of iron deficiency. Limitations of MCV include cases where the underlying cause is due to a combination of factors - such as iron deficiency (a cause of microcytosis) and vitamin B12 deficiency (a cause of macrocytosis) where the net result can be normocytic cells.

Microcytic Anemia:

If the MCV value is less than 80fl the type of anemia is called as Microcytic Anemia.

Microcytic anemia is primarily a result of hemoglobin synthesis failure or insufficient production, which could be caused by several etiologies include

·         Heme synthesis defect

·         Iron deficiency anemia 

·         Anemia of chronic disease (more commonly presenting as normocytic anemia but may rarely appear as microcytic)

·         Globin synthesis defect

·         Alpha-thalassemia

·         Beta-thalassemia

·         HbE syndrome (Rare condition)

·         HbC syndrome (Rare condition)

·         Sideroblastic defect

·         Hereditary sideroblastic anemia

·         Acquired sideroblastic anemia, including lead toxicity

Macrocytic Anemia

If the MCV value is more than 101fl the type of anemia is called as Macrocytic Anemia. Macrocytic anemia can be further divided into "Megaloblastic Anemia" or "Non Megaloblastic macrocytic anemia".

Megaloblastic Anemia

·         Megaloblastic anemia, the most common cause of macrocytic anemia, is due to a deficiency of either vitamin B₁₂, folic acid, or both. Deficiency in folate and/or vitamin B₁₂ can be due to either inadequate intake or insufficient absorption.

·         Pernicious anemia is caused by a lack of intrinsic factor (IF), which is required to absorb vitamin _B12 from food. A lack of intrinsic factor may arise from an autoimmune condition targeting the parietal cells (atrophic gastritis) that produce intrinsic factor or against intrinsic factor itself. These lead to poor absorption of vitamin _B12.

Non Megaloblastic Macrocytic Anemia

• Hypothyroidism
• Alcoholism 
• Liver disease 
• Drugs such as Methotrexate, zidovudine, and other substances may inhibit DNA replication such as heavy metals (e.g. Lead)

                                   

Normocytic Anemia:

Normocytic anemia occurs when the overall hemoglobin levels are decreased, but the red blood cell size (mean corpuscular volume) remains normal. Causes include:

·         Acute blood loss

·         Anemia of chronic disease

·         Aplastic anemia (bone marrow failure)

·         Hemolytic anemia

Dimorphic Anemia

A dimorphic appearance on a peripheral blood smear occurs when there are two simultaneous populations of red blood cells, typically of different size and hemoglobin content. For example, a person recently transfused for iron deficiency would have small, pale, iron deficient red blood cells (RBCs) and the donor RBCs of normal size and color. Similarly, a person transfused for severe folate or vitamin B12 deficiency would have two cell populations, but, in this case, the patient's RBCs would be larger and paler than the donor's RBCs. Evidence for multiple causes appears with an elevated RBC distribution width (RDW), indicating a wider-than-normal range of red cell sizes.

Classification of Anemia on the basis of etiology (Cause)

1.      Decrease Production

·         Pure red cell aplasia

·         Aplastic anemia

·         Anemia of renal failure by insufficient erythropoietin production

·         Pernicious anemia

·         Anemia of folic acid deficiency and with vitamin B₁₂, causes megaloblastic anemia

·         Iron deficiency anemia, resulting in deficient heme synthesis

·         Thalassemias, causing deficient globin synthesis

·         Myelodysplastic syndrome

Increased Destruction

Anemias of increased red blood cell destruction are generally classified as hemolytic anemias. These are generally featuring jaundice and elevated lactate dehydrogenase (LDH) levels.

·         Hereditary spherocytosis

·         Hereditary elliptocytosis

• Enzyme deficiencies
• Pyruvate kinase and hexokinase deficiencies causing defect glycolysis
• Glucose-6-phosphate dehydrogenase (G₆PD) deficiency and glutathione synthetase deficiency causing increased oxidative stress
• Hemoglobinopathies
• Sickle cell anemia
• Hemoglobinopathies causing unstable hemoglobins
• Paroxysmal nocturnal hemoglobinuria

·         Warm autoimmune hemolytic anemia

·         Cold agglutinin hemolytic anemia

·         Infections including malaria

·         Hemodialysis

Blood loss

·         Accidents

·         Surgery

·         Gastro intestinal tract bleeding

·         Heavy menstruation

General signs and symptoms of anemia

Most commonly, people with anemia report feelings of weakness, or fatigue, and sometimes poor concentration. They may also report dyspnea (shortness of breath) on exertion. In very severe anemia, the body may compensate for the lack of oxygen-carrying capability of the blood by increasing cardiac output.

On examination, the signs exhibit pallor (pale skin, mucosal linings, conjunctiva and nail beds). There may be signs of specific causes of anemia, e.g., koilonychia (in iron deficiency), jaundice (when anemia results from abnormal break down of red blood cells — in hemolytic anemia), bone deformities (found in thalassemia major)

In severe anemia, there may be signs of a hyperdynamic circulation: tachycardia (a fast heart rate).

Chronic anemia may result in behavioral disturbances in children as a direct result of impaired neurological development in infants, and reduced scholastic performance in children of school age. Restless legs syndrome is more common in those with iron-deficiency anemia.