D47: Other neoplasms of uncertain or unknown behaviour of lymphoid, haematopoietic and related tissue

D47.3: Essential (haemorrhagic) thrombocythaemia

The bone marrow is inside bone. The blood cells are formed in the bone marrow of some of the bones. There are 3 different types of blood cell: red blood cells, white blood cells and platelets. Red blood cells are important for carrying oxygen in the blood. White blood cells are part of the body’s immune system. They fight pathogens. Platelets are important for clotting blood.

Your bone marrow produces too many platelets. Having too many platelets makes it easier for blood clots to form. The blood clots can then block blood vessels. The tissue can be damaged as a result. This means you can have visual disturbances or pain in your fingers and toes, for example. You can also sometimes have small bleeds, in the skin for example.