Platelet Function Testing

Coagulation

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Description

Studies of platelet function are used to identify and help diagnose platelet dysfunction. Testing may consist of:

Platelet Function Analysis (PFA100): This is a non-specific screening test of platelet function and von willebrand's factor activity.   Using disposable test cartridges citrated whole blood is aspirated through a microscopic aperture cut into a biologically active membrane at the end of a capillary. The membranes of the cartridges are coated with collagen and adenosine diphosphate (ADP) or collagen and epinephrine inducing a platelet plug to form which closes the aperture.

Aggregation studies by light transmission aggregation (LTA): Platelet rich plasma (PRP) is stirred in a cuvette at 37°C and the cuvette sits between a light source and a photocell. When various agonists are added, the platelets aggregate and absorb less light and so the transmission increases and this is detected by the photocell and recorded as a trace of percentage light transmission versus time. The aggregation trace produced will depend on the agonist used, its strength and if any dysfunction is present.

Secretion studies: chemi-luminescence measurement of ATP release form platelet dense granules.

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Indications

Studies of platelet function are undertaken in patients suspected of having a platelet function defect (PFD). Suspicion may include symptoms such as excessive bleeding or bruising; unexpected or prolonged bleeding or bruising, investigation of petechiae or purpura (small purple/red dots in the skin caused by bleeding from small vessels); frequent nosebleeds, heavy menstrual bleeding, bleeding gums, excessive bleeding during dental procedures, etc.

A screening test (PFA100) is available on demand (24/7 availability). This should be the first line test requested in patients suspected of a PFD. An abnormal result may suggest a PFD or possible von willebrand's disease. If indicated (upon discussion with the haemostasis and thrombosis team) more specific aggregation and secretion studies may be requested.

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Sample Type

PFA - 2 x sodium citrate samples, received within 4 hours of venipuncture. Must not be sent through a pneumatic delivery tube.
LTA and secretion studies - citrated plasma, however special sample bottles are required to be taken under controlled conditions. Please contact the haemophilia center.

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Reference Range

As indicated on the report.

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Turnaround Time

Within 2 hours (final report within 48 hours)

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Testing Frequency

PFA - on demand available 24/7. All treated as urgent upon receipt by laboratory.
Aggregation and secretion studies are not routine tests and require medical discussion before requesting. The patient MUST be referred to the Haemophilia and Thrombosis Center, who in turn will arrange a suitable time for testing with the laboratory.

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External Notes

For platelet aggregation and secretion studies the patient must be referred to Sheffield Haemophilia and Thrombosis Center.

All samples must be hand delivered to the coagulation laboratory.

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Patient Preparation

Patients may be instructed to refrain from taking drugs that can affect the function of normal platelets and hence the results of these tests, such as aspirin, non-steroidal anti-inflammatory drugs (NSAIDs), or any over-the-counter medications that contai

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References

Harrison et al.and British Committee for Standards in Haematology (2011), Guidelines for the laboratory investigation of heritable disorders of platelet function. British Journal of Haematology, 155: 30-44.
Gresele P. (2015). Diagnosis of inherited platelet function disorders: guidance from the SSC of the ISTH.J Thromb Haemost. 2015 Feb;13(2):314-22. doi: 10.1111/jth.12792. Epub 2015 Jan 22.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.