Anemia, which is defined as a reduction in the number of circulating erythrocytes, is a common manifestation of primary bone marrow disorders, primary abnormalities of erythrocytes, immunologic disorders, nutritional deficiencies, and a broad spectrum of systemic diseases that secondarily result in anemia.

The basic mechanisms of anemia can be divided into those conditions that result in accelerated destruction or loss of RBCs and those in which the primary abnormality is impaired ability of the bone marrow to produce sufficient numbers of erythrocytes to replace those that are lost.

Anemias due to impaired production of erythrocytes by the bone marrow.

Erythropoietin deficiency.

Quantitative deficiency of hematopoietic stem cells and/or committed erythroid progenitor cells.

Impaired ability of erythroid progenitors to respond to erythropoietin.

Disorders characterized by impaired dna synthesis: megaloblastic anaemia

Impaired hemoglobin synthesis: disorders characterized by diminished heme synthesis.

Impaired hemoglobin synthesis: disorders characterized by impaired globin synthesis--thalassemias.

Ineffective erythropoiesis.

Anemias due to accelerated destruction, consumption, or loss of circulating erythrocytes.

The specific signs and symptoms of anemia may vary widely from patient to patient with the same degree and tempo of anemia.

Mild anemia often is associated with no clinical symptoms and may be discovered only when a complete blood cell count is done for another reason.

The earliest clinical symptoms of mild to modest anemia

Weakness, fatigue, lethargy, decreased stamina, palpitations, dyspnea on exertion, and orthostatic light-headedness are common symptoms in patients with chronic anemia.