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Anemia Defined and Classified

Anemia is defined as reduced oxygen carrying capacity of the blood. Functionally, anemia arises when there is insufficient hemoglobin or the hemoglobin is not functional. The physiologic function of hemoglobin is to deliver oxygen to the tissues. Oxygen binds to hemoglobin as the blood passes through the lungs and is then released to the tissues as the blood circulates throughout the rest of the body. When hemoglobin is not adequate for oxygenation of the tissues, tissue hypoxia results.
In true operational terms, anemia is defined as a reduction in the total number of red blood cells (RBCs), amount of hemoglobin circulating, and RBC mass. RBCs, hemoglobin, hematocrit, RBC indices, and RDW are measured/calculated by the use of laboratory instrumentation and the obtained results are then compared to reference ranges as well as the previously established baseline for that patient.
Symptoms of anemia may include:
  • Fatigue
  • Pale skin
  • A fast or irregular heartbeat
  • Shortness of breath
  • Chest pain
  • Dizziness
  • Cognitive problems
  • Cold hands and feet
  • Headache
The presence of anemia is detected by measurement of RBCs, hemoglobin, and hematocrit. These parameters are then compared to established reference intervals that include consideration of variables such as age, gender, and race. Borderline anemic individuals may not be diagnosed by evaluating these three parameters alone. In order to make an appropriate diagnosis, blood smear evaluation, reticulocyte count, RBC indices, and RBC distribution width should be included.

There are three major methods for classifying anemias. These are:

  1. Classification of anemias based on mean cell (corpuscular) volume (MCV) and red cell distribution width (RDW)
  2. Morphologic classification
  3. Pathophysiologic classification
The following table categorizes anemias according to MCV and RDW.

RDW (Heterogeneity)
Microcytic homogenous
Microcytic heterogenous
Normocytic homogenous
Normocytic heterogenous
Macrocytic homogenous
Macrocytic heterogeous