Causes

Thrombocytopenia means you have fewer than 150,000 platelets per microliter of circulating blood. Because each platelet lives only about 10 days, your body normally renews your platelet supply continually by producing new platelets in your bone marrow.

Thrombocytopenia rarely is inherited; or it can be caused by a number of medications or conditions. Whatever the cause, circulating platelets are reduced by one or more of the following processes: trapping of platelets in the spleen, decreased platelet production or increased destruction of platelets.

Trapped platelets

The spleen is a small organ about the size of your fist situated 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 — can harbor too many platelets, which decreases the number of platelets in circulation.

Decreased production of platelets

Platelets are produced in your bone marrow. Factors that can decrease platelet production include:

• Leukemia and other cancers
• Some types of anemia
• Viral infections, such as hepatitis C or HIV
• Chemotherapy drugs and radiation therapy
• Heavy alcohol consumption

Increased breakdown of platelets

Some conditions can cause your body to use up or destroy platelets faster than they're produced, leading to a shortage of platelets in your bloodstream. Examples of such conditions include:

• Pregnancy. Thrombocytopenia caused by pregnancy is usually mild and improves soon after childbirth.
• Immune thrombocytopenia. Autoimmune diseases, such as lupus and rheumatoid arthritis, cause this type. The body's immune system mistakenly attacks and destroys platelets. If the exact cause of this condition isn't known, it's called idiopathic thrombocytopenic purpura. This type more often affects children.
• Bacteria in the blood. Severe bacterial infections involving the blood (bacteremia) can destroy platelets.
• Thrombotic thrombocytopenic purpura. This 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 impairs kidney function.
• Medications. Certain medications can reduce the number of platelets in your blood. Sometimes a drug confuses the immune system and causes it to destroy platelets. Examples include heparin, quinine, sulfa-containing antibiotics and anticonvulsants.