Haemoglobin, the red pigment in the red blood cells is essential for the transport of oxygen to the tissue. If the level is below the normal range, the person is anaemic, looks pale and tires easily. Severe anaemia can lead to heart failure. Anaemia can be due to a) decresed production of normal red blood cells b) lack of essential nutrients like iron c) hereditary disorders like thalassemia. Additional tests may be needed to confirm this.