Heparin-induced thrombocytopenia
| Heparin-induced thrombocytopenia | |
|---|---|
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| A schematic drawing of platelet factor 4, which when bound to heparin leads to an immune response in HIT. | |
| Classification and external resources | |
| Specialty | hematology |
| ICD-10 | D69.5 |
| ICD-9-CM | 289.84 |
| MedlinePlus | 000556 |
| eMedicine | article/1357846 |
Heparin-induced thrombocytopenia (HIT) is the development of thrombocytopenia (a low platelet count), due to the administration of various forms of heparin, an anticoagulant. HIT predisposes to thrombosis, the abnormal formation of blood clots inside a blood vessel, and when thrombosis is identified the condition is called heparin-induced thrombocytopenia and thrombosis (HITT). HIT is caused by the formation of abnormal antibodies that activate platelets. If someone receiving heparin develops new or worsening thrombosis, or if the platelet count falls, HIT can be confirmed with specific blood tests.
The treatment of HIT requires both protection from thrombosis and choice of an agent that will not reduce the platelet count further. Several alternatives are available for this purpose and mainly used are danaparoid, fondaparinux, argatroban and bivalirudin
While heparin was discovered in the 1930s, HIT was not reported until the 1960s.
Heparin may be used for both prevention and the treatment of thrombosis. It exists in two main forms: an "unfractionated" form that can be injected under the skin or through an intravenous infusion, and a "low molecular weight" form that is generally given subcutaneously (administered under the skin). Commonly used low molecular weight heparins are enoxaparin, dalteparin, nadroparin and tinzaparin.
In HIT, the platelet count in the blood falls below the normal range, a condition called thrombocytopenia. However, it is generally not low enough to lead to an increased risk of bleeding. Most people with HIT will therefore not experience any symptoms. Typically the platelet count will fall 5–14 days after heparin is first given; if someone has received heparin in the previous three months, the fall in platelet count may occur sooner, sometimes within a day.
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