Thrombocytopenia is the medical term that refers to a low or reduced platelet count. Platelets are cells in the blood that enable the blood to clot and prevent the loss of red blood cells, which carry oxygen through the body. Platelets are lost even in healthy bodies during normal bodily functions, but they are replaced with new platelets produced in the bone marrow. Thrombocytopenia occurs either when platelets are not replaced at the same rate as loss or when abnormal destruction of platelets occurs.

Thrombocytopenia can cause abnormal bleeding, especially from the nose and in the stomach and intestines. Signs of thrombocytopenia may include nosebleeds, unexplained vaginal bleeding, or vomiting blood. Thrombocytopenia can be diagnosed through routine blood work and a complete blood count, which also measures the levels of red and white blood cells. In some cases, testing the bone marrow may also be necessary. During a physical examination, the spleen may also be checked for enlargement.

The causes of thrombocytopenia can include disease, infection, and medication. Thrombocytopenia can originate in the bone marrow, in the blood stream, or outside of the blood stream. Thrombocytopenia is most often a result of chemotherapy and radiation, and occasionally affects patients taking heparin. A low platelet count does not necessarily indicate disease and is sometimes secondary to another condition.

When the bone marrow is producing platelets at a normal rate, but platelet counts are low in the blood stream, this is often the result of an infection that is destroying the platelets faster than they are produced. This condition is known as Idiopathic Thrombocytopenic Purpura (ITP).

Thrombocytopenia caused by reduced production in the bone marrow is more severe than destruction of platelets as in ITP. However, any signs of thrombocytopenia, including unexplained bleeding from the nose, gums, or lower legs or the appearance of blood in vomit or stool should be brought to the attention of a physician. People with thrombocytopenia are at a high risk of abnormal or severe bleeding, including internal hemorrhaging. Treatment for thrombocytopenia depends on the cause, but may include steroids or other medication and may require platelet transfusions.