Platelets are cells that are formed in the bone marrow to help the blood clot properly. Approximately 150,000 to 450,000 platelets should be found in 1 microliter of blood. Many medical conditions and chemical substances can cause low blood platelet levels. This condition is known as thrombocytopenia and must be corrected to prevent excessive bleeding.
Reduced Platelet Production
Low blood platelet levels can be caused by reduced platelet production in the bone marrow. Several medical conditions can cause reduced platelet production. Aplastic anemia causes the bone marrow to stop the production of new blood cells. Cancer causes bone marrow damage and can destroy cells. Chemotherapy and radiation therapy for cancer also destroy cells. Viruses such as mumps, rubella and parvovirus can all cause decreased platelet production. Platelet levels usually return to normal once these viruses have been cleared by the immune system. Substances such as prescription drugs and alcohol can also cause reduced platelet production. Diuretics and some antibiotics are known to slow down platelet production. Heavy drinkers may experience temporary drops in platelet count due to excessive alcohol consumption.
Platelet Destruction
In some people with low platelet counts, the bone marrow functions normally and produces the right amount of platelets. However, these platelets can be destroyed by some medical conditions. Widespread infections and viruses can lead to low platelet counts. Mononucleosis is an example of a virus that can cause the destruction of platelets. The National Heart Lung and Blood Institute reports that 5 percent of pregnant women experience decreased platelet counts shortly before delivery. The cause for this reduction in platelets is not known. Autoimmune diseases cause the immune system to destroy the platelets in the body. Rheumatoid arthritis and lupus are examples of platelet-destroying autoimmune diseases. Platelets are destroyed when they are passed through blood vessel grafts, bypass machines and blood transfusion tubing. Some antibiotics and seizure medications also cause platelet destruction.
Spleen Enlargement
Platelets are often held in the spleen. When the spleen is working properly, it does not hold on to too many platelets. When the spleen is enlarged, it can hold on to more platelets than needed. This causes a reduced number of platelets in the blood. Severe liver conditions such as liver cancer and cirrhosis can cause an enlarged spleen. Bone marrow conditions that reduce the body's ability to make new cells can also cause an enlarged spleen.
