If for any reason your blood platelet count falls below normal, the condition is called thrombocytopenia. Normally, you have anywhere from 150,000 to 450,000 platelets per microliter of circulating blood. Because each platelet lives only about 10 days, your body continually renews your platelet supply by producing new platelets in your bone marrow.

Thrombocytopenia has many possible causes.

Trapping of platelets in the spleen

The spleen is a small organ about the size of your fist located just below your rib cage on the left side of your abdomen. Normally, your spleen works to fight infection and filter unwanted material from your blood. An enlarged spleen — which can be caused by a number of disorders — may harbor too many platelets, causing a decrease in the number of platelets in circulation.

Reduced production of platelets

Platelets are produced in your bone marrow. A disease or condition that involves your bone marrow, such as leukemia and some types of anemia, could lead to a reduction in the number of new platelets produced. Viral infections, including HIV infection, may reduce your bone marrow's ability to make platelets. Toxic chemicals, chemotherapy drugs and heavy alcohol consumption also can reduce platelet production.

Increased breakdown of platelets

A number of conditions can cause your body to use up or destroy platelets more rapidly than they are produced, leading to a shortage of platelets in your bloodstream. Examples include:

  • Pregnancy. Being pregnant may cause mild thrombocytopenia.
  • Idiopathic thrombocytopenic purpura (ITP). In ITP, your body's immune system mistakenly identifies platelets as a threat and forms antibodies that attack them.
  • Autoimmune diseases. Other diseases in which your body's immune system attacks healthy tissue may cause thrombocytopenia. Examples include lupus and rheumatoid arthritis.
  • Bacteria in the blood. Severe bacterial infections involving the blood (bacteremia) may lead to destruction of platelets.
  • Thrombotic thrombocytopenic purpura (TTP). TTP is a rare condition that occurs when small blood clots suddenly form throughout your body, using up large numbers of platelets.
  • Hemolytic uremic syndrome. This rare disorder causes a sharp drop in platelets, destruction of red blood cells and impairment of kidney function. Sometimes it can occur in association with a bacterial Escherichia coli (E. coli) infection, such as may be acquired from eating raw or undercooked meat.
  • Medications. Certain medications can reduce the number of platelets in your blood by confusing the immune system and causing it to destroy platelets. Examples include heparin, quinidine, quinine, sulfa-containing antibiotics, interferon, anticonvulsants and gold salts.
Apr. 06, 2012