Anemia: Introduction

Anemia is a reduction in the mass of circulating red blood cells. Generally, people are considered anaemic when their haemoglobin levels are more than two standard deviations below the mean level in their hospital’s laboratory. The diagnosis of anaemia is influenced by variables such as the patient’s age (neonates are anaemic at levels of haemoglobin that would be considered polycythemic in some adults), pregnancy status (haemodilution in pregnancy lowers measured haemoglobin), residential altitude, and ethnic or racial background.
Symptomatic anaemia exists when Hb content is less than that required to meet the oxygen-carrying demands of the body. If anaemia develops slowly, however, there may be no functional impairment even though the Hb is less than 7g/100ml of blood.
Anaemia is not a disease but rather a symptom of other illness.