Trapping of platelets in the spleen, reduced production of platelets, and increased platelet breakdown can all lead to low platelet count, according to Mayo Clinic. 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.
Under normal circumstances, about one-third of the platelets remain in the spleen. Injury or disease that causes swelling of the spleen increases the number of platelets it retains, according to the National Heart, Blood, and Lung Institute. Cancer, liver disease and scarring of the bone marrow sometimes cause enlargement of the spleen.
Excessive alcohol consumption or the presence of toxic substances in the body limits platelet production, according to Mayo Clinic. Viral infections, including HIV, also slow the body's ability to produce more platelets as the old ones die. Chemotherapy, anemia and leukemia also reduce the production of platelets.
When the body breaks down platelets faster than it is able to replace them, the result is a low platelet count, according to Mayo Clinic. Conditions leading to this problem range from pregnancy to autoimmune diseases. Some medications confuse the body and cause it to attack the blood platelets. When an individual has a severe bacterial infection in the blood, his body sometimes begins attacking the platelets as a part of the immune system response.