According to the National Heart Lung and Blood Institute, a high platelet count can indicate a number of different conditions, including cancer, anemia or a reaction to medications. The National Heart Lung and Blood Institute (NHLBI) explains that there are two different types of thrombocythemia, or a high volume of platelets in the blood. Primary thrombocythemia is caused by faulty bone marrow stem cells, while secondary thrombocythemia is caused by some other underlying physical condition.
The NHLBI states that the causes of primary thrombocythemia are unknown. However, in some cases, primary thrombocythemia can be passed genetically from parent to child. By contrast, a wide range of conditions and illnesses can cause secondary thrombocythemia, including anemia, adverse reactions to medication and tuberculosis. Additionally, inflammatory diseases, such as inflammatory bowel syndrome, can also lead to an overabundance of platelets in the blood. In some cases, a high platelet count can indicate cancer. People who have had their spleen removed surgically may also produce too many platelets.
According to the NHLBI, under certain circumstances, secondary thrombocythemia can be a temporary condition. For example, an acute infection, physical activity and serious blood loss may cause the platelet count to rise. However, in such cases, the platelet count usually returns to normal after a short time.