In this Stago Educational Talk, Peter Baker, Clinical Scientist at Oxford Haemophilia and Thrombosis Centre, breaks down all the essentials of Heparin-Induced Thrombocytopenia (HIT) laboratory testing, following the British Society of Haematology guideline: "Diagnosis and management of heparin-induced thrombocytopenia (Third edition). It now includes functional assays in the diagnosis of (HIT), when to use direct-acting oral anti-coagulants, and more. Heparin-Induced Thrombocytopenia is a complex immune-mediated adverse reaction to heparin therapy, leading to decreased platelet counts and an increased risk of thrombosis. Early and accurate diagnosis is crucial for effective management and improved patient outcomes.