USE: Haemoglobin is the oxygen-carrying component contained in red blood cells (RBCs). It is composed of a single protein called globin and a compound called haem, which contains iron atoms and the red pigment porphyrin. The oxygen-combining capacity of the blood is directly proportional to the haemoglobin concentration, rather than to the number of RBC. Haemoglobin determination is part of a complete blood count that screens for disease associated with anaemia, determines the severity of anaemia, follows the response to treatment for anaemia and evaluates polycythemia. Anaemia is defined as Hb below normal for age and gender. Use of Test: Suspected anaemia or erythrocytosis.