Heparin Induced Thrombocytopenia (HIT)
HIT may occur in 1%–3% of patients receiving heparin for a week or more. HIT is most often encountered in the following populations:
- Those with cardiovascular disease and interventions
- Orthopedic surgery patients
- Medically compromised patients
However, HIT may occur in any population. HIT results when a patient receives heparin (a blood thinner) and antibodies then form that cause damage to the lining of blood vessels as well as to platelets. When this happens, the platelets aggregate or clump together. This causes consumption of platelets, resulting in a fall in the patient’s platelet count. This damage to the blood vessel lining and clumping of the platelets can lead to development of blood clots despite the presence of heparin. It is unclear why some patients on heparin develop this problem.
The fall in platelet count with HIT usually develops 5 to 7 days following the start of heparin for the first time. However, HIT may occur within 1–3 days in patients who have been previously exposed to heparin or sensitized in the recent past (usually within 3 months). Once heparin is stopped, the platelet count should begin to recover in 2–5 days. However, despite the discontinuation of the heparin, the patient may be at continued high risk of thrombosis for the next 30 days, and alternate anticoagulation may be required dependent on the patient’s clinical circumstances. There are several medications specifically indicated and licensed for treating HIT such as Refludan®, Argatroban® and Danaparoid®. The use of low molecular weight heparin (LMWH) as an alternative anticoagulant after the diagnosis of HIT is established is not recommended.
The diagnosis of suspected HIT should be made based upon a clinical assessment made by a medical care provider experienced with this problem, in conjunction with a variety of specialized laboratory tests. One commonly used test is a HIT assay. If HIT is confirmed, all heparin must be stopped. This includes the removal of heparin-coated catheters and the discontinuation of all heparin flushes of catheters.
