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What are the complications of HIT?

Thrombocytopenia with a platelet count fall of more than 50% is the most common clinical effect of HIT, occurring in over 90% of HIT patients during heparin treatment (1,2). Despite the thrombocytopenia, bleeding complications are rare and HIT is strongly associated with thrombosis.

The absolute risk of thrombosis in a HIT patient is between 50 and 75%. HIT patients presenting with thrombocytopenia alone (without apparent thrombus - isolated HIT) have a high risk of thrombosis despite discontinuation of heparin. The rate of thrombosis is about 5-10% per day over the first 1-2 days; the cumulative risk over 30 days is about 50% (1,2).

The thromboembolic complications associated with HIT are listed below:

Thromboembolic complications associated with HIT (2)

Venous thrombosis
  • Deep vein thrombosis
  • Pulmonary embolism
  • Adrenal haemorrhagic infarction (thrombosis in adrenal veins)
  • Cerebral venous (dural sinus) thrombosis
  • Thrombosis in hepatic and retinal veins (less common)

Arterial thrombosis
  • Most commonly involves the distal aorta or major arteries of the lower limbs leading to limb ischaemia
  • Myocardial infarction
  • Acute ischaemic stroke
  • Less common, but well described events:
      - Mesenteric artery thrombosis (bowel infarction)
      - Brachial artery thrombosis (upper limb gangrene)
      - Renal artery thrombosis

Other thrombosis
  • Graft and prosthetic device thrombosis
  • Extracorporeal circuit thrombosis

The localisation of thrombosis in HIT is strongly influenced by clinical factors. There is a marked predominance of venous thrombosis when HIT occurs in surgical patients, whilst arterial thrombosis is more likely in HIT patients with cardiovascular disease(2).

The more unusual or severe the thrombotic event in patients receiving heparin the more likely the thrombosis is caused by HIT(2).

1.Greinacher A. Heparin-Induced thrombocytopenia: recognition, treatment and prevention. An overview of clinical presentation, pathogenesis, diagnosis and treatment. Thromb Haemost 2004; 92(suppl):42-5

2.Warkentin TE. Clinical Picture of HIT. In: Warkentin TE and Greinacher A, eds. Heparin-induced thrombocytopenia  4th edition, New York, Informa Healthcare, 2007;21-66

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