Thrombocytopenia is a condition marked by low platelet (thrombocyte) count in the blood. The platelet count in a healthy individual is from 150,000 to 400,000  platelets per microliter. The condition is often diagnosed when an individual has less than 150,000 platelets present in each microliter of blood circulating in their body. Platelets are the colorless cells in the blood responsible for making blood clots.
Thrombocytopenia is caused by the destruction of the number of platelets in the blood or reduction of platelet production. Platelets are short-lived cells produced in the bone marrow, from where they are transported into the bloodstream. As a result, a persistent shortage of platelets may be caused by diseases affecting the bone marrow such as leukemia. Thrombocytopenia may also be induced by certain medications and therapies.
The most common cause of thrombocytopenia is an immune disorder called immune thrombocytopenia (ITP), formerly known as idiopathic thrombocytopenic purpura. This condition prevents blood from clotting normally. Low blood platelets can also happen because they are prevented from reaching the blood. Enlargement of the spleen can cause platelets to be trapped, reducing the number in circulation. Autoimmune disorders can also cause antibodies to target one’s platelets as though they were fighting off an infection.
Thrombocytopenia occurs in both children and adults. The presented symptoms range from mild to debilitating. Mild cases of thrombocytopenia do not usually present obvious symptoms and are normally discovered through blood tests. Bleeding (internal or external) is the most common sign of thrombocytopenia. Internal hemorrhaging may result in death, but this usually occurs in severe cases where the platelet count is less than 10,000 per microliter of blood.
This article explains some of the telltale signs of thrombocytopenia.