Heparin Induced Thrombocytopenia (HIT)

Exam Cram

• Heparin induced thrombocytopenia (HIT) has two types, type 1 is not immune mediated & type 2 is

• Presentation: thrombocytopenia post heparin introduction

• Antibodies: anti- PF4

• Management: stop heparin, start fondaparinux or bivalirudin 

Outline

Background

• There are two types of HIT

  • Type 1: mild non immune reaction, occurring within 48hrs of heparin and normalises without intervention, no associated thrombosis risk

  • Type 2: immune reaction to heparin causing platelet destruction after 5 days requiring intervention due to increased thrombosis risk

Assessment

History

• Thrombocytopenia post heparin introduction

• Asymptomatic 

Examination

• Petechial rash, 

• Mucosal bleeding- epistaxis

• Thrombosis (arterial or venous), skin necrosis

Investigations

• Thrombocytopenia

• anti- PF4 antibodies

Scores

• 4Ts: thrombocytopenia ( < 50% reduction), timing, thrombosis, other causes: predicts <5% to 60% chance 

Diagnosis

Diagnostic criteria: clinical

Differentials: thrombocytopenia

• Immune Thrombocytopenic Purpura Diagnosis of exclusion if HIT ruled out

• Thrombotic Thrombocytopenic Purpura (TTP) Unwell, focal neurology

• Liver Cirrhosis Liver will consume platelets

• Disseminated Intravascular Coagulation (DIC) Raised INR, low fibrinogen

• Haemolytic Uraemic Syndrome Raised creatinine, haemolysis

Management

Type 1: < 48hrs, nil intervention

Type 2:  > 5 days, stop heparin, start fondaparinux or bivalirudin

Resources and References

1. Nicolas D, Nicolas S, Hodgens A, et al. Heparin-Induced Thrombocytopenia. [Updated 2023 May 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482330/

2. Ahmed I, Majeed A, Powell R. Heparin induced thrombocytopenia: diagnosis and management update. Postgrad Med J. 2007 Sep;83(983):575-82. doi: 10.1136/pgmj.2007.059188. PMID: 17823223; PMCID: PMC2600013.

Written in 2025