Master Heparin Induced Thrombocytopenia (HIT) with Picmonic for Medicine

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Heparin Induced Thrombocytopenia (HIT)

Hippie-heron HIT Trombone-side-toe-peanut
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The most common cause of drug-induced thrombocytopenia with an incidence of 0.2 to 5.0% in patients who have been treated with heparin for greater than 4 days. Unfractionated heparin is more likely to cause HIT than Low Molecular Weight Heparin (LMWH).
9 KEY FACTS
PATHOPHYSIOLOGY
5-10 Days After Heparin Exposure
Nickel and Dime drinks during Heparin Day

Thrombocytopenia (decreased platelets >50%) typically occurs 5-10 days following initiation of heparin therapy. Early onset of HIT (within ~10.5 hours) may be seen in patients who have received heparin therapy recently and have persistent antibodies to the complex of heparin and platelet factor 4.

Heparin-Platelet Factor 4 Complex
Hippie-heron with Plate and (4) Fork

Platelet Factor 4 is released from the alpha granules of platelets upon platelet activation and binds to heparin.

Autoantibodies Form Against Complex
Ant-tie-body Getting Defensive

IgG, IgA and IgM autoantibodies form against the Heparin-Platelet Factor 4 complex.

Heparin-Platelet Factor 4-Antibody Complex Binds Platelets
Hippie-heron with Plate (4) Fork and Ant-tie-body Binding to Plates

This process leads to the disease sequelae of platelet aggregation and thus thrombocytopenia and procoagulant product which can lead to thrombosis.

Platelet Aggregation
Sticky Plates

Heparin-Platelet Factor 4-antibody complex bound to platelets results in platelet aggregation, subsequent removal from circulation and thus thrombocytopenia.

Procoagulant Release
Pro-clog

The platelet aggregation also results in the release of procoagulants which can cause thrombosis.

SYMPTOMS
Thrombocytopenia
Trombone-side-toe-peanut

Platelets fall by >50%; however, the platelet count is usually still >20,000 platelets.

DIAGNOSIS
Serotonin Release Assay (SRA)
Silver-tonic Releasing SRA-tap

The Serotonin Release Assay (SRA) is the gold standard. The diagnosis of HIT is confirmed if high serotonin release occurs as this is a marker of platelet activation. A CBC is always performed to determine the degree of thrombocytopenia.

TREATMENT
Stop Heparin, Start Direct Thrombin Inhibitor
Red-light Hippie-heron, Green-light Direct-route Trombone Inhibitor

Heparin must be stopped immediately and a direct thrombin inhibitor, such as bivalirudin or argatroban should be started.

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