Heparin-Induced Thrombocytopenia (HIT)

Question 1

What is initially seen in HIT?

Answer 1

Platelet count drops around 5-14 days after the initial exposure to heparin

Question 2

Which type of heparin is HIT more commonly seen with?

Answer 2

IV unfractionated heparin

- incidence much lower with LMWH

Question 3

What is Type 1 HIT, how does platelet count react, and what treatment is required?

Answer 3

Non-immune, transient, asymptomatic thrombocytopenia

• platelet levels usually remain above 80
• no treatment required
• platelet count improves spontaneously, even when heparin is continued

Question 4

What is Type 2 HIT?

Answer 4

Rare but serious autoimmune condition, caused by heparin use, which may result in multi-organ failure + death
- autoimmune haemoloytic anaemia + thrombocytopenia

Question 5

How is Type 2 HIT caused?

Answer 5

Immune reaction against complex of heparin + factor IV
Complexes are removed from circulation = thrombocytopenia
Factor IV is released into the circulation and activates remaining platelets = thrombosis
The result is coexistent thrombocytopenia and thrombosis, in both arteries and veins

Question 6

How is Type 2 HIT treated?

Answer 6

Heparin stopped immediately, alternative used

Thrombolytic agents, e.g. streptokinase, may be necessary if significant thrombosis