Anaemia is caused by many factors. The most obvious is when haemorrhage occurs, and there is noticeable loss of bright red blood. This may result from accidents when a major blood vessel is injured and blood simply pours out. In fact, if an artery is severed, the blood gushes forth in spurts that may reach a metre in height. Unless the bleeding is stopped promptly and the blood replaced, the person can quickly suffer from circulatory failure and die.
More commonly blood loss is insidious and probably unnoticed. Many women suffer from menstrual periods that are longer and heavier than normal, and gradually develop anaemia.
But other factors that are needed for the normal formation of the blood cells may be deficient. For instance iron (essential for haemoglobin formation), vitamin B12, folic acid, vitamin C, protein and thyroxine may not be present in adequate amounts. This may all predispose to anaemia.
The bone marrow itself may be defective, as in a plastic anaemia. Here the causes may be unknown, or it may be adversely affected by the action of certain drugs or simply lack of adequate amounts of the blood-forming elements. The marrow may be destroyed by the action of irradiation, and so fail to produce normal blood cells.
In some cases the marrow is infiltrated by cancer cells that have come from a primary source in some other part of the body, such as the breast. Gradually the cell-forming tissue is destroyed, as anaemia of increasing severity develops. Leukaemia and myelomatosis may have a similar effect on the marrow.
In some patients there may be a greatly increased rate of destruction of the red cells once they have been formed. This was probably most notable in years gone by in babies suffering from Rh incompatibility.
Red cell destruction occurred at an enormous, rapid and disastrous rate. Unless the entire blood was removed by repeated “exchange transfusions” soon after birth, the infant’s life was imperilled. Fortunately, preventive measures have now largely made this a disaster of a bygone era, but all doctors well remember the events that were relatively corn- Electron micrograph of three types of cells found in human blood: at left is a red blood cell or erythrocite, a biconcave disc; a white blood cell (centre), which is spherical with microvilli projecting from its surface; the wafer like cell at right is a blood platelet.