The Mayo Clinic defines thrombocytopenia as the clinical term for having a low blood platelet count. Platelets are a type of cell that circulates in the bloodstream throughout the body. They perform a crucial function by clumping together in response to bleeding, causing a blood clot. The blood clot formed by the platelets plug the hole in the blood vessel and stem the bleeding. There are a few distinct types of thrombocytopenia, which are categorized based on their cause.
Idiopathic Thrombocytopenic Purpura
This type of thrombocytopenia is also sometimes called immune thrombocytopenic purpura. Regardless of whether "idiopathic" or "immune" is used in the name, the condition is often abbreviated as ITP. The Lucile Packard Children's Hospital at Stanford reports that the exact cause of ITP is unknown--hence the name "idiopathic," which means "unknown." People diagnosed with ITP often have a viral infection two to three weeks before the drop in platelets. Scientists speculate that the immune system inadvertently destroys the platelets when building up immunity toward the virus in an attempt to clear the infection. ITP causes red or purple skin bruising, called purpura. In addition, petechia may occur, which is when the bruising manifest as many small red or purple spots on the skin. Other signs and symptoms include bleeding of the gums; blood present in stool, urine, and/or vomit; and nosebleeds.
Thrombotic Thrombocytopenic Purpura
The National Heart Lung and Blood Institute describes in detail the features of thrombotic thrombocytopenic purpura, often abbreviated TTP. Like ITP, TTP also involves a low blood platelet count. However, the low blood platelet count of TTP is caused by abnormal blood clots formed by platelets in the blood vessels throughout the body. When this condition is severe, most of a person's platelets are stuck in blood clots throughout the body and aren't available to form a blood clot as a result of injury. The tiny blood clots caused by TTP may be visible as petechia, as in ITP. If a blood clot forms in the blood vessels of the brain, a life-threatening stroke may result.
Drug-induced thrombocytopenia occurs when drugs are the cause of the low blood platelet count. MedlinePlus, an online medical encyclopedia sponsored by the U.S National Library of Medicine, reports two main subtypes of drug-induced thrombocytopenia: immune and non-immune. Certain drugs may cause the body to mistakenly attack and destroy blood platelets, which is the case in immune drug-induced thrombocytopenia. Non-immune drug-induced thrombocytopenia occurs when a drug causes the body to produce fewer platelets than normal. Chemotherapeutic drugs used to treat cancer are common causes of non-immune drug-induced thrombocytopenia. The signs and symptoms of this type of thrombocytopenia are similar to the other two types: formation of petechia on the skin; skin that bruises easily; and easily bleeding gums and frequent heavy nosebleeds.