Heparin Induced Thrombocytopenia

Question 1

What is the definition of HIT?

Answer 1

• immune mediated thrombocytopenia that can result in acute venous or arterial thrombosis

IMP: do NOT confuse with non-immune thrombocytopenia, which is heparin associated (relatively mild decrease in platelets)

Question 2

What is the mechanism of the non-immune heparin associated thrombocytopenia?

Answer 2

• passive coating and elimination of platelets exposed to pharmaceutical heparin
• not associated with risk of thrombosis

Question 3

What is the hallmark of HIT?

Answer 3

• decline in platelet count after the initiation of heparin
• develops anywhere from 5-14 days after initiation
• may occur within 24 hours if patient received heparin within 100 days
• drop in platelets of 50% or development of absolute thrombocytopenia (<150 k)

Question 4

How long can the HIT antibodies persist?

Answer 4

• about 3 months

Question 5

When do platelets start to recover after the discontinuation of heparin?

Answer 5

• return to normal within a few days

Question 6

What is the most common clinical presentation of HIT?

Answer 6

• venous thrombosis
  *DVT, PE, adrenal hemorrhage, venous associated limb gangrene, cerebral venous thrombosis
• can also present with arterial or micro thrombosis
• skin necrosis and erythematous plaques can occur at injection sites

IMP: bleeding complications are unusual

Question 7

What type of Heparin is most often associated with HIT?

Answer 7

• unfractionated Heparin
• LMWH can also cause HIT but it is less frequent