After each chemotherapy course for your wife's AML, you will have noticed that her platelet count falls. This is a result of the chemotherapy temporarily damaging the cells in the bone marrow that make her platelets. The blood count usually picks up after a few weeks as these bone marrow cells recover. In the meantime she needs transfusions of platelets to keep her platelet count up to a safe level. In most people, the donated platelets last several days so they only need platelet transfusions once or twice a week.

The problem that you are describing is only seen very occasionally but can be quite difficult to deal with. It sounds as though your wife is 'refractory' to the standard platelets she has been getting, making them less effective. This can happen for two groups of reasons:

• non-immune causes: for example, when somebody has a temperature, they use up platelets faster; some medicines, like the antifungal drug amphotericin, lower the platelet count; or if a patient has a big spleen, the platelets may collect there, rather than circulate in the blood. Chemotherapy that is given nowadays tends to be more intensive. In some patients this may mean that the white cells or the platelets or both can take several weeks to recover. If there is no leukaemia left the platelet count should eventually recover.
• immune causes, where the patient's immune system recognises the platelets as different, attacks them and destroys them very quickly. This is more often seen in people who have had lots of blood and platelet transfusions or in women who have been pregnant. This is due to the greater number of different tissue types - the blood donors' or the babies' - that they have been exposed to. Everybody has a 'tissue type', this is a group of proteins on the surface of every cell in their body, including blood cells. The exact combination of proteins is inherited, although some unrelated people may share a tissue type. When a person's immune system meets a different tissue type, as during a blood or platelet transfusion, it may make antibodies to that foreign tissue type. These can then react with platelets in future transfusions, if these platelets have one of these different tissue types, making them useless.

To find out which of these groups is the likely cause of her problem, your wife's doctors can do a blood test to see whether she has any antibodies to different tissue types present. If she does, it should be possible to find blood donors who share her tissue type. Her immune system is unlikely to reject these platelets as they are so similar to her own. Because of this, they may work better than the standard platelets that she has been having. If these tissue type 'matched platelets' do not work, there may be other blood tests necessary to identify a cause. You will need to discuss this situation with your specialist who can advise on possible ways of managing the low platelet count .