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Thrombocytopenia is the medical term for a low blood platelet count. Platelets (thrombocytes) are colorless blood cells that play an important role in blood clotting. They stop blood loss by clumping together at the site of a blood vessel injury and forming plugs in vessel holes.

If for any reason your blood platelet count falls below normal, this is called thrombocytopenia. Complications may range from none at all to severe bleeding.

Thrombocytopenia often occurs as a result of a separate disease or disorder. For example, a bone marrow disorder such as leukemia can interfere with platelet production and reduce the number of platelets in your blood. Or sometimes, thrombocytopenia occurs because of an immune system malfunction that develops for unknown reasons. In addition, thrombocytopenia may occur as a reaction to a medication.

Thrombocytopenia often improves by treating the underlying cause. In some situations, medications or surgery can help treat chronic thrombocytopenia. If bleeding is severe, you may need a blood transfusion.

Signs and symptoms of a low blood platelet count may include:

• Easy or excessive bruising
• Superficial bleeding into the skin that appears as a rash of pinpoint-sized reddish-purple spots (petechiae), usually on the lower legs
• Prolonged bleeding from cuts
• Spontaneous bleeding from your gums or nose
• Blood in urine or stools
• Unusually heavy menstrual flows
• Profuse bleeding during surgery

Serious or widespread bleeding indicates an emergency and requires immediate care.

Normally, you have anywhere from 150,000 to 450,000 platelets per microliter of circulating blood. Although each platelet lives only about 10 days, your platelet supply is continually renewed by production of new platelets from your bone marrow.

If for any reason your blood platelet count falls below normal, the condition is called thrombocytopenia. Complications may range from none at all to severe bleeding. The risk of bleeding increases as the number of platelets decreases. The greatest risk is when platelet count falls very low — below 10,000 platelets per microliter. At this point, internal bleeding may occur despite a lack of any injury, although this is rare.

Causes of a low platelet count generally fall under one of the several categories:

Reduced production of platelets
Platelets are produced in your bone marrow. A medical problem that involves your bone marrow, such as occurs with leukemia and some types of anemia, could lead to a reduction in the number of new platelets produced. Viral infections, including HIV infection, may suppress your bone marrow's ability to make platelets. Other cancers that affect bone marrow, chemotherapy drugs and heavy alcohol consumption also can impair 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, which may cause mild thrombocytopenia.
• Idiopathic thrombocytopenic purpura (ITP), a condition in which your immune system mistakenly identifies platelets as a threat and forms antibodies that attack them.
• Other autoimmune diseases, such as lupus and rheumatoid arthritis, which may lead to destruction of platelets due to a malfunctioning immune system.
• Blood poisoning (septicemia) from severe bacterial infections, which may lead to destruction of platelets.
• Thrombotic thrombocytopenic purpura (TTP), a rare, life-threatening condition that occurs when small blood clots suddenly form throughout your body, using up large numbers of platelets. TTP can happen sporadically or as a side effect of some medications.
• Hemolytic uremic syndrome, another rare disorder that causes a sharp drop in platelets, destruction of red blood cells and impairment of kidney function. Sometimes, this can occur in association with a bacterial Escherichia coli (E. coli) infection, such as may be acquired from eating raw or undercooked meat (often hamburger).

Sometimes, certain medications can cause a thrombocytopenic reaction by confusing the immune system and causing it to destroy platelets. Examples include heparin, quinidine, quinine, sulfa-containing antibiotics, some oral diabetes drugs, gold salts and rifampin. Sometimes, heparin-induced thrombocytopenia can cause excessive blood clotting instead of bleeding, increasing the risk of clot formation deep within a leg blood vessel or the transport of such a clot to your lungs, which can be life-threatening.

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 your left side. 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.

If you have abnormal bleeding or bruising, or if you develop a rash of pinpoint-sized red spots (petechiae), see your doctor. Because some of the underlying causes of thrombocytopenia are serious, it's important for your doctor to promptly evaluate any signs or symptoms.

Also, see your doctor promptly if you're taking heparin and you have severe or increasing pain in your leg. This may be an indication of a blood clot deep in a vein in your leg, which can seriously affect your health.

Mild thrombocytopenia often causes no signs or symptoms. A routine blood test may show that your platelet count is low even though you haven't been experiencing problems. If you have a condition that puts you at risk of thrombocytopenia, your doctor may monitor your platelet count to make sure it doesn't fall too low.

If you've noticed possible signs and symptoms of thrombocytopenia, such as easy bruising or excessive bleeding, your doctor will likely obtain a platelet count from a blood test and examine your blood under a microscope. Your doctor may also order special blood tests and a bone marrow examination to help determine the cause.

As a first step toward treatment, your doctor will want to identify the underlying cause of thrombocytopenia. If you have a fever in addition to a low platelet count, this may indicate you have an infection. A physical examination may reveal an enlarged spleen that may be entrapping platelets.

Mild thrombocytopenia often has no long-lasting effects. The biggest risk of severe thrombocytopenia is bleeding into the brain or digestive tract, which although rare, can be life-threatening. Complications more often arise from the conditions that cause thrombocytopenia. For example, the kidney failure that accompanies hemolytic uremic syndrome may require lifelong treatment if damage to the kidneys is permanent.

Sometimes, treatment for low platelet count isn't necessary, particularly in children. In these cases, the bone marrow may make up for the shortage of platelets by producing large numbers of new ones until the initiating cause subsides. Young platelets are especially active in clotting, so even though the total concentration of platelets is low, your child may not experience any bleeding problems and need no special treatment. Mild thrombocytopenia in pregnant women usually improves soon after childbirth.

If your doctor can identify the cause of thrombocytopenia, then the approach is treat the underlying condition or stop using the problem medication.

Treating thrombocytopenia may involve several options:

• Medications. For idiopathic thrombocytopenic purpura, treatment may include medications that block the antibodies that attack platelets, such as corticosteroids, or medications that suppress the immune system to reduce antibody formation, such as cyclophosphamide (Cytoxan) or azathioprine (Imuran).
• Surgery. Sometimes, removing the spleen (splenectomy) relieves signs and symptoms or helps improve chronic idiopathic thrombocytopenic purpura that doesn't respond to corticosteroids.
• Blood transfusions and plasma exchange. For severe bleeding, your doctor can replace lost blood with transfusions of packed red blood cells. Platelet concentrates are given to treat severe thrombocytopenia, particularly those related to cancer or chemotherapy.

Thrombotic thrombocytopenic purpura requires emergency treatment with plasma exchange therapy or therapeutic plasmapheresis. If you have hemolytic uremic syndrome, you may need kidney dialysis in addition to red blood cell and platelet transfusions.

If your platelet count is low, your doctor may recommend avoiding drugs such as aspirin that may impair platelet function and avoiding excessive alcohol intake. You may also wish to avoid contact sports, which can put you at a higher risk of injury and bleeding.