Heparin Induced Thrombocytopenia

Thrombosis Canada Guidelines - HIT

• Overview of heparin induced thrombocytopenia including diagnosis and treatment recommendation

4T Score

• Scoring tool used to assess clinical probability of heparin induced thrombocytopenia. This tool helps determine whether thrombocytopenia is due to heparin or another cause.

  • Pretest probability:

    • 0-3: low risk

    • 4-5: intermediate risk

    • 6-8: high risk

  • Tool is better at ruling out HIT than ruling it in

1. Which of the following describes the underlying mechanism behind heparin induced thrombocytopenia (HIT)? 

a) Heparin directly activates platelets 

b) Platelet factor 4 (PD4) binds heparin resulting in platelet activation 

c) Heparin inhibits platelet aggregation 

d) PF4 binds platelets resulting in platelet activation

2. Which of the following statements is FALSE regarding type II HIT? 

a) Occurs 1-4 days following heparin exposure 

b) Type II HIT is Immune mediated  

c) Most likely to result in venous thrombosis compared to arterial 

d) Characterized by ≥50% decrease in platelet count 

3. Which of the following is NOT a common finding of HIT? 

a) Bleeding 

b) Thrombosis  

c) Shortness of breath 

d) Chills 

4. True or false: HIT is more common with unfractionated heparin than LMWH?

a) True

b) False

5. What is the treatment strategy for type II HIT? 

a) Continue heparin 

b) Discontinue heparin and initiate non-heparin anticoagulant 

c) Discontinue heparin and initiate platelet transfusion 

d)  Discontinue heparin and initiate thrombolytic