Platelet function screening (PFA-100)

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:

● Interaction with collagen-captured VWF to form the initial barrier to blood loss
● Propagate the clot via platelet aggregation
● Provide the platform for secondary haemostasis
● Localisation mechanisms
● 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. "
Reference range: 

Collagen/ADP 60 - 200
Collagen/epinephrine 90 - 200

Sample type and Volume required: 
External requests:1.6mL whole blood citrate x 2 aliquots
Internal requests: please refer to EPR label
Turnaround time: 
4 hours
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.

Diagnostic Haemostasis and Thrombosis Department
020 7188 2797
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 13/09/2019