The erythron is defined as the total mass of circulating erythrocytes and their precursors within the bone marrow.

Alterations in the erythron are common in clinical practice, and developing an approach to interpreting these abnormalities is important. Initial assessment of the erythron is generally accomplished through evaluation of a complete blood cell count (CBC). Major alterations include anemia and erythrocytosis. On the basis of CBC results, clinical history, and physical examination, additional diagnostic tests can then be selected to further characterize these abnormalities in an attempt to identify a specific underlying pathophysiologic process.