Anaemia is defined as haemoglobin concentration in blood below the lower limit of the normal range for the age and sex of the individual. In adults, the lower extreme of the normal haemoglobin is taken as 13 g% for males and 11.5% for females. New born infants have higher haemoglobin levels and therefore, 15% is taken as the lower limit at birth, whereas at 3 months, the lower limit is taken as 9.5%. Although haemoglobin value is employed as the only parameter for determining whether or not anaemia is present, the red cell counts, haematocrit(PCV) and absolute values (MCV, MCH and MCHC) provide alternate means of assessing anaemia.

The symptoms of anaemia are:

Tiredness
Easy fatiguability
Generalized muscular weakness
Lethargy
Headache

In older patients- there maybe symptoms of cardiac failure, angina pectoris, intermittent claudication, confusion and visual disturbances.

In an anaemic person, subnormal level of haemoglobin causes lowered oxygen- carrying capacity of the blood. This in turn, initiates compensatory physiologic adaptations such as:

Increased release of oxygen from haemoglobin,
Increased blood flow to the tissues,
Maintainance of the blood volume and
Redistribution of blood flow to maintain the cerebral blood supply.

Eventually, however, tissue hypoxia (lack of oxygen) develops causing impaired functions of the affected tissues. The degree of functional impairment of individual tissues is variable depending upon their oxygen requirements. Tissues with high oxygen requirement such as the heart, CNS and the skeletal muscle during exercise, bear the brunt of clinical effects of anaemia.

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