Low platelet count can be caused by acquired or inherited conditions, which may cause the body's bone marrow to decrease platelet production, according to the National Heart, Lung, and Blood Institute. The body may destroy or use up the platelets, or the spleen holds on to too many platelets. The blood normally has between 150,000 and 450,000 platelets per microliter. Each platelet lives about 10 days, so the body is continually replacing them.
The National Heart, Lung, and Blood Institute states that cancer, aplastic anemia, exposure to toxic chemicals, medicines, alcohol, genetic conditions and viruses can cause bone marrow to slow or stop production of platelets. Toxic chemicals such as arsenic, pesticides and benzene can also slow the production of platelets. Cancers such as leukemia and lymphoma destroy bone marrow, which leads to a reduction in platelet production.
The body may destroy its own platelets because of autoimmune diseases such as lupus and rheumatoid arthritis, according to the National Heart, Lung, and Blood Institute. Infections such as mononucleosis or cytomegalovirus also contribute to the destruction of platelets. The body may destroy platelets and cause a low count because of surgery, medicines and pregnancy.
Approximately one-third of platelets are held in the spleen. An enlarged spleen may hold to too many platelets, which results in a decreased circulation of platelets in the bloodstream, according to the National Heart, Lung, and Blood Institute. Conditions related to an enlarged spleen are cirrhosis and myelofibrosis.