A condition in which the concentration of the oxygen-carrying pigment haemoglobin in the blood is below normal. Haemoglobin molecules are carried inside red blood cells and transport oxygen from the lungs to the tissues. Normally, stable haemoglobin concentrations in the blood are maintained by a balance between red-cell production in the bone marrow and red-cell destruction in the spleen. Anaemia may result if this balance is upset. Anaemia is not a disease but a feature of many different disorders. There are various types, which can be classified into those due to decreased or defective red-cell production by bone marrow (see anaemia, aplastic; anaemia, megaloblastic; anaemia, iron-deficiency) and those due to decreased survival of the red cells in the blood (see anaemia, haemolytic). The severity of symptoms depends on how low the haemoglobin concentration has become. Slightly reduced levels can cause headaches, tiredness, and lethargy. Severely reduced levels can cause breathing difficulty on exercise, dizziness, angina, and palpitations. General signs include pallor, particularly of the skin creases, the lining of the mouth, and the inside of the eyelids. Anaemia is diagnosed from the symptoms and by blood tests (see blood count; blood film). A bone marrow biopsy may be needed if the problem is with red blood cell production.


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