The word anemia, literally means the deficiency of red blood cells or hemoglobin.
A person is considered anemic, if he or she has a low hemoglobin level for their age and sex.
Anemia is not a disease in itself, but rather an expression of an underlying disorder.
There are many etiological causes for anemia. It can be classified them according to the red cells’ microscopic appearance or by the causative mechanisms.
Classification According To The Morphology
According to the microscopic appearance of red blood cells, we can divide anemia’s causes into four.
They are hypochromic microcytic anemias, normochromic normocytic anemias, macrocytic anemias, and anemias with abnormal red cell morphologies.
The average red cell is about the size of a small lymphocyte.
Cells are considered microcytic or macrocytic compared to that.
Comments about the colour of cells are made considering the extent of the central pale area.
Normal cells exhibit a central pale area of one-third of the cell size. If it exceeds 50%, the cells are considered hypochromic.
Iron deficiency anemia, anemia of chronic disease, sideroblastic anemia, and thalassemia are examples for hypochromic microcytic anemias, and the normochromic normocytic anemias include blood loss, stem cell defects, renal dysfunctions, aplastic anemia, and anemia of some chronic diseases.
Causes for macrocytic anemias include folic acid and vitamin B12 deficiencies, hypothyroidism, and drug-induced anemias, while hereditary spherocytosis, hemoglobinopathies, autoimmune hemolytic anemia, and some enzyme deficiencies fall under anemias with abnormal red cell morphologies.
Classification According To The Mechanism
Various conditions cause anemia through different mechanisms. We can also use these mechanisms in classifying anemia. The mechanisms are,
- Decreased production,
- Increased hemolysis, and
- Loss of blood.
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Hypothyroidism, nutritional deficiencies like iron deficiency or folic acid deficiency, chronic kidney disease, and aplastic anemia are examples of decreased production.
Causes for hemolytic anemias include sickle cell anemia, hereditary spherocytosis, hemolytic uremic syndrome, malaria, and disseminated intravascular coagulation.
Anemia due to blood loss can be due to acute causes like traumatic accidents, or some long-standing causes like gastrointestinal bleeding or having heavy periods, which is known as menorrhagia.
Diagnostic Approach
Getting answers for some important questions in a patient’s history, examination, and investigations helps to navigate in the correct pathway of diagnosing the cause for anemia.Â
An anemic patient’s major signs and symptoms are pallor, tiredness, shortness of breath, and fatigue.
These are very vague features, and further investigations are needed to come to a diagnosis.
Full blood count, peripheral blood smear, iron studies, and sometimes even bone marrow studies may be needed considering the clinical suspicion.Â
The lower limits for hemoglobin levels for males and females are 13.5 mg/dL and 11.5 mg/dL, respectively. The mean corpuscular volume of an anemic patient is used to differentiate between types of anemias.
[<80fL – microcytic] (microcytic if the MCV falls under 80 femtolitres,)
[80-95fl – normocytic] (normocytic if the MCV is between 80 to 95 femtolitres, and)
[>95fl – macrocytic] (macrocytic if the MCV goes beyond that.)
These tests, together with clinical features, helps to have an idea about the severity and the type of anemia.
If a patient gets a very low hemoglobin count with no stainable iron in bone marrow studies, the results point towards severe iron deficiency anemia.
On the other hand, if a patient shows abnormally large misshapen cells in a peripheral blood smear with features of neurological abnormalities in clinical history, we can think of megaloblastic anemia.Â
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