Platelet function screening (PFA-100)
- Description
- Anticoagulated whole blood is passed into a thin-bore capillary at arterial pressure towards a collagen membrane impregnated with either ADP or epinephrine. The membrane contains a pore with a diameter of 150μm. The collagen reproduces exposure of VWF and platelets to damaged vessel endothelium whilst the ADP or epinephrine agonists mimic localised activation. Normally functioning platelets should occlude the pore within reference ranges for what is termed the 'closure time' whilst reduced platelet numbers or function, and most sub-types of von Willebrand disease, will generate prolonged closure times.
- Clinical details
- Platelets are anucleate fragments of the cytoplasm of their parent cell, the megakaryocyte. They circulate predominantly at the margins of blood vessels in a dormant, resting state, but are capable of a rapid and dramatic response to various stimuli arising from vessel trauma. They have a complex structure that facilitates their specialised functions, of which the main ones are listed below: â— Interaction with collagen-captured VWF to form the initial barrier to blood loss â— Propagate the clot via platelet aggregation â— Provide the platform for secondary haemostasis â— Localisation mechanisms â— Maintain endothelial junction integrity Exposure of sub-endothelial collagen after vessel trauma promotes binding of VWF which tethers platelets via their GpIb receptor. Blood flow rolls the platelet over where it forms stable associations via separate collagen binding receptors which also serves to activate the platelet. Activated platelets change their shape to promote effective physical interaction and release of the contents of cytoplasmic granules which activate more platelets and promote platelet-to-platelet aggregation via fibrinogen bridging of receptors on adjacent platelets. Biochemical pathways are also activated to promote aggregation, and the phospholipid membrane re-organises to promote localisation of secondary haemostasis to stabilise the platelet plug. Reduced platelet numbers, receptor deficiency/dysfunction, granule deficiency or granule content deficiency, biochemical abnormalilties and drug interactions can lead to bleeding disorders. "
- Related condition
- Reference range
- Collagen/ADP 60 - 200 Collagen/epinephrine 90 - 200
- Units
- seconds
- Testing site
- Synnovis : Blood Sciences : St Thomas' Hospital
- Laboratory
- Diagnostic Haemostasis and Thrombosis
- Sample type and volume required
- External requests:1.6mL whole blood citrate x 2 aliquots Internal requests: please refer to EPR label
- Special sample instructions
The sample should be analysed within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling creates a dilution error and leads to inaccurate results.
- Turnaround time
- 4 hours
- Contacts
Diagnostic Haemostasis and Thrombosis Department
St Thomas’ Hospital
Phone: 020 7188 2797
St Thomas’ Hospital
North Wing – 4th and 5th Floors
Westminster Bridge Road
London SE1 7EHGuy’s Hospital
Phone: 020 7188 7188 ext. 53860
Guy’s Hospital
Southwark Wing – 4th Floor
Great Maze Pond
London SE1 9RT
Outside core hours, contact Duty Haemostasis Biomedical Scientist