What Causes Thrombocytopenia?

A number of factors can cause thrombocytopenia (a low platelet count). The condition can be inherited (passed from parents to children), or it can develop at any age. Sometimes the cause isn't known.

In general, a low platelet count occurs because:

• The body's bone marrow doesn't make enough platelets.
• The bone marrow makes enough platelets, but the body destroys them or uses them up.
• The spleen holds onto too many platelets.

A combination of the above factors also may cause a low platelet count.

The Bone Marrow Doesn't Make Enough Platelets

Bone marrow is the sponge-like tissue inside the bones. It contains stem cells that develop into red blood cells, white blood cells, and platelets. When stem cells are damaged, they don't grow into healthy blood cells.

Several conditions or factors can damage stem cells.

Cancer

Cancer, such as leukemia (lu-KE-me-ah) or lymphoma (lim-FO-ma), can damage the bone marrow and destroy blood stem cells. Cancer treatments, such as radiation and chemotherapy, also destroy the stem cells.

Aplastic Anemia

Aplastic anemia is a rare, serious blood disorder in which the bone marrow stops making enough new blood cells. This lowers the number of platelets in your blood.

Toxic Chemicals

Exposure to toxic chemicals, such as pesticides, arsenic, and benzene, can slow the production of platelets.

Medicines

Some medicines, such as diuretics and chloramphenicol, can slow the production of platelets. Chloramphenicol (an antibiotic) is rarely used in the United States.

Common over-the-counter medicines, such as aspirin or ibuprofen, also can affect platelets.

Alcohol

Alcohol also slows the production of platelets. A temporary drop in platelets is common among heavy drinkers, especially if they're eating foods that are low in iron, vitamin B12, or folate.

Viruses

Chickenpox, mumps, rubella, Epstein-Barr virus, or parvovirus can decrease your platelet count for a while. People who have AIDS often develop thrombocytopenia.

Genetic Conditions

Some genetic conditions, such as Wiskott-Aldrich and May-Hegglin syndromes, can cause low numbers of platelets in the blood.

The Body Destroys Its Own Platelets

A low platelet count can occur even if the bone marrow makes enough platelets. The body may destroy its own platelets due to autoimmune diseases, certain medicines, infections, surgery, pregnancy, and some conditions that cause too much blood clotting.

Autoimmune Diseases

With autoimmune diseases, the body's immune system destroys its own platelets. One example of this type of disease is called idiopathic thrombocytopenic purpura, or ITP.

In most cases, the body's immune system is thought to cause ITP. Normally, your immune system helps your body fight off infections and diseases. But if you have ITP, your immune system attacks and destroys its own platelets—for an unknown reason.

Other autoimmune diseases that destroy platelets include lupus and rheumatoid arthritis.

Medicines

A reaction to some medicines can confuse your body and cause it to destroy its platelets. Any medicine can cause this reaction, but it happens most often with quinine, antibiotics that contain sulfa, and some medicines for seizures, such as Dilantin,^® vancomycin, and rifampin.

Heparin is a medicine commonly used to prevent blood clots. But an immune reaction may trigger the medicine to cause blood clots and thrombocytopenia. This condition is called heparin-induced thrombocytopenia (HIT). HIT rarely occurs outside of a hospital.

In HIT, the body's immune system attacks a substance formed by heparin and a protein on the surface of the platelets. This attack activates the platelets and they start to form blood clots. Blood clots can form deep in the legs, or a clot can break loose and travel to the lungs.

Infection

A low platelet count can occur after blood poisoning from a widespread bacterial infection. A virus, such as mononucleosis or cytomegalovirus, also can cause a low platelet count.

Surgery

Platelets can be destroyed when they pass through man-made heart valves, blood vessel grafts, or machines and tubing used for blood transfusions or bypass surgery.

Pregnancy

About 5 percent of pregnant women develop mild thrombocytopenia when they're close to delivery. The exact cause isn't known for sure.

Rare and Serious Conditions That Cause Blood Clots

Some diseases can cause a low platelet count. Two examples are thrombotic thrombocytopenic purpura (TTP) and disseminated intravascular clotting (DIC).

TTP is a rare blood condition. It causes blood clots to form in the body's small blood vessels, including vessels in the brains, kidneys, and heart.

DIC is a rare complication of pregnancy, severe infections, or severe trauma. Tiny blood clots form suddenly throughout the body.

In both conditions, the blood clots use up many of the blood's platelets.

The Spleen Holds On to Too Many Platelets

Usually, one-third of the body's platelets are held in the spleen. If the spleen is enlarged, it will hold on to too many platelets. This means that not enough platelets will circulate in the blood.

An enlarged spleen is often due to severe liver disease—such as cirrhosis (sir-RO-sis) or cancer. Cirrhosis is a disease in which the liver is scarred. This prevents it from working properly.

An enlarged spleen also may be due to a bone marrow condition, such as myelofibrosis (MI-eh-lo-fi-BRO-sis). With this condition, the bone marrow is scarred and isn't able to make blood cells.