Platelet fibrinogen antigen

Platelets are concentrated, washed and then lysed with a detergent. Fibrinogen in the supernatant is measured in a sandwich ELISA. The fibrinogen is captured by antibodies bound to microtitre plate wells, incubated, and unbound material then washed off. A solution of antibody to fibrinogen that is conjugated to an enzyme is added to ‘tag’ onto any captured fibrinogen. Unbound conjugate is washed off and a substrate for the enzyme is added, the product of the enzyme-substrate reaction being coloured. Colour intensity is in direct proportion to the degree of conjugate-binding, itself proportional to the amount of fibrinogen capture.
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. Fibrinogen is contained within alpha granules and measurement of platelet fibrinogen can aid diagnosis of alpha graule disorders.
Reference range: 

3.3 - 7.6

mg/dl 1012 plt
Sample type and Volume required: 
Contact laboratory.
Turnaround time: 
Contact laboratory
Special sample instructions: 

50 ml of fresh blood is taken into citrate/EDTA anticoagulant and delivered directly to the laboratory for immediate manipulation.

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: 07/08/2015