Heparin induced thrombocytopenia (HIT) screen

Chemiluminescent immunoassay for the detection of IgG Anti-PF4/Heparin antibodies
Clinical details: 
Approximately 5% of patients on unfractionated heparin therapy develop type 2 heparin-induced thrombocytopenia (HIT). Some of the platelet factor 4 (PF4) released from activated platelets binds to the platelet surface, to which heparin will bind. This causes a conformational change in the PF4 and exposes neoepitopes which are immunogenic and can lead to antibody production. The thrombocytopenia arises from removal of antibody-coated platelets from the circulation by the reticuloendothelial system. Bleeding is rarely a problem yet conversely, thrombosis is a recognised complication because antibody binding activates platelets to form platelet aggregates, further reducing the platelet count. Procoagulant microparticles are generated and excess PF4 not bound to heparin instead binds to endothelial heparan sulphate which can lead to further antibody formation and immune complex-mediated endothelial damage, which can progress to thrombosis or DIC. Type 1 HIT is not immune mediated but caused by mild direct platelet activation by heparin and is ostensibly benign. HIT can occur in LMWH therapy but is less common. HIT is largely a clinical diagnosis but laboratory assays are valuable for confirmation or exclusion.
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Synonyms or keywords: 
Sample type and Volume required: 
Citrated platelet poor plasma (500µL x 1 aliquot).
Internal requests: please refer to EPR label
Turnaround time: 
5 days - Call laboratory to arrange urgent analysis
Special sample instructions: 

The sample should be analysed or processed & stored within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling or overfilling creates a dilution error and leads to inaccurate results.

Storage and transport: 
It is advised that citrated plasma is frozen prior to transport and sent to the laboratory on dry ice to maintain sample quality and integrity.
Diagnostic Haemostasis and Thrombosis Department
St Thomas': 020 7188 2797; Guy's: 020 7188 7188 ext. 53860
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times

Guy's Hospital
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT

Outside core hours, contact Duty Haemostasis Biomedical Scientist
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 09/07/2021