Heparin-Induced Thrombocytopenia

Suspect HIT when a patient exposed to unfractionated heparin or low-molecular-weight heparin develops a platelet fall of at least 50% from baseline, particularly with new arterial or venous thrombosis between days 5 and 14 after starting heparin. This timing rule applies even when thrombocytopenia or thrombosis develops after heparin has already been discontinued. ScienceDirect+1ScienceDirectTreatment and Prevention of Heparin-Induced Thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition) - ScienceDirectWolters KluwerHeparin-Induced Thrombocytopenia in Patients...

Typical immune HIT begins 5-10 days after exposure, with a reported range of 4-15 days; delayed-onset presentations may occur after exposure has ended. A new thrombosis during this interval increases pretest probability and should prompt both diagnostic testing and immediate anticoagulant substitution rather than observation for platelet recovery. BMJ+2BMJHeparin-induced thrombocytopenia - Symptoms, diagnosis and treatment | BMJ Best PracticeacpjournalsDelayed-Onset Heparin-Induced ThrombocytopeniaScienceDirectTreatment and Prevention of Heparin-Induced Thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition) - ScienceDirect

Obtain a current platelet count, review the pre-heparin baseline and daily trajectory, identify every heparin source, and assess for new thrombosis. The immediate clinical decision is driven by the 4Ts domains: magnitude of thrombocytopenia, timing, thrombosis or other sequelae, and competing causes of thrombocytopenia. WileyWileyGuidelines on the diagnosis and management of heparin‐induced thrombocytopenia: second edition

Apply the 4Ts score before ordering or interpreting HIT assays. Its four components are thrombocytopenia severity, timing relative to heparin, thrombosis or other HIT sequelae, and the likelihood of another explanation. A low score supports excluding HIT without laboratory testing; a non-low score requires laboratory evaluation alongside therapeutic action. WileyWileyGuidelines on the diagnosis and management of heparin‐induced thrombocytopenia: second edition

Order a PF4/heparin antibody immunoassay for intermediate- or high-probability HIT. A positive immunoassay does not independently establish HIT because the diagnosis requires a compatible clinical syndrome plus heparin-dependent platelet-activating antibodies; antibody positivity without clinical manifestations is insufficient. BMJBMJHeparin-induced thrombocytopenia - Symptoms, diagnosis and treatment | BMJ Best Practice

Use a functional platelet-activation assay, such as the serotonin-release assay (SRA), to establish whether detected antibodies are pathogenic when immunoassay findings and clinical probability require confirmation. The SRA detects pathogenic HIT antibodies, and quantitative PF4 enzyme-immunoassay optical-density interpretation may help contextualize results, but neither should override the clinical picture. Wiley+1WileySerotonin‐release assay‐negative heparin‐induced ...WileySerotonin‐release assay‐positive but platelet factor 4 ...

For suspected HIT with at least intermediate 4Ts probability, immediately stop all heparin exposures and start a non-heparin anticoagulant. Do not await confirmatory testing, because stopping heparin alone is inadequate to prevent ongoing thrombotic risk. BMJBMJHeparin-induced thrombocytopenia - Symptoms, diagnosis and treatment | BMJ Best Practice

Do not initiate or continue a vitamin K antagonist as sole therapy in acute HIT. ACCP guidance recommends an alternative non-heparin anticoagulant over continued UFH or LMWH and over initiation or continuation of vitamin K antagonist therapy in strongly suspected or confirmed HIT, whether or not thrombosis is present. ScienceDirectScienceDirectTreatment and Prevention of Heparin-Induced Thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition) - ScienceDirect

Choose the non-heparin anticoagulant according to acuity, procedure needs, renal replacement therapy, organ function, monitoring capability, and formulary availability. U.S.-available agents described for HIT include intravenous argatroban and bivalirudin, which require laboratory-based dose adjustment, and subcutaneous fondaparinux, which does not require routine monitoring. NEJMNEJMFondaparinux for Heparin-Induced Thrombocytopenia | NEJM Clinician

When transitioning from parenteral therapy to a direct oral anticoagulant, reported timing is within 2 hours after stopping argatroban or bivalirudin, 8-12 hours after stopping danaparoid, and 24 hours after the last fondaparinux dose. In severe renal impairment, DOAC dose selection and safety remain uncertain, favoring individualized selection of an alternative regimen when necessary. PubMedPubMedManagement of Heparin-Induced Thrombocytopenia - PMC

If warfarin is selected after acute HIT, overlap with parenteral non-heparin anticoagulation for at least 5 days and until the target INR is reached. Argatroban and bivalirudin can prolong the INR, so interpret INR during transition with this pharmacologic effect in mind. PubMedPubMedManagement of Heparin-Induced Thrombocytopenia - PMC

For remote HIT requiring VTE treatment or prophylaxis, ASH recommends a non-heparin anticoagulant rather than UFH or LMWH; listed options include apixaban, dabigatran, edoxaban, rivaroxaban, fondaparinux, danaparoid, and a vitamin K antagonist. ASHASHAmerican Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia | Blood Advances | American Society of Hematology