Anemia (also spelled anaemia) is a decrease in the total amount of red blood cells (RBCs) or hemoglobin in the blood, or a lowered ability of the blood to carry oxygen. When anemia comes on slowly, the symptoms are often vague and may include feeling tired, weakness, shortness of breath, and a poor ability to exercise. Symptoms may include fatigue, skin pallor, shortness of breath, light-headedness, dizziness or a fast heartbeat. Anaemia is a condition in which the number of red blood cells or the haemoglobin concentration within them is lower than normal. In men, anemia is typically defined as hemoglobin level of less than 13.5 gram/100 ml and in women as hemoglobin of less than 12.0 gram/100 ml. Some individuals with anemia have no symptoms. Others with anemia may: tiredness, Weakness, Fatigue, Appearing pale. This may be due to a reduction in the number of red blood cells caused by decreased production, blood loss, increased destruction or a combination of these factors. It may also be due to abnormally formed haemoglobin or abnormal red blood cells, which affect the stability of the cells, making them more prone to destruction.