Platelet function studies

Last updated: Wednesday, 05, December, 2007

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Item Process
Specimen

Citrated blood; collection by laboratory staff.

Ideally the patient should not have taken aspirin or other NSAID in the week prior to testing.
It is also best to avoid any garlic in food for at least 2 days.

Method

Platelet Aggregometry:

Platelet-rich plasma stirred at 37°C with continuous recording of light transmission.
Aggregating agent added; aggregation results in decreasing optical density.
The platelet release reaction is assessed by the presence of secondary aggregation with ADP, adrenaline; aggregation with collagen, arachidonate.
The release reaction can be measured by prior incubation of platelet-rich plasma with labelled serotonin, and measurement of radioactivity in supernatant plasma following aggregation or using other reagents.

Platelet Function Analyser (PFA-100):

In recent years PFA-100 has become widely available as a simpler technique to screen for platelet function abnormalities.

A PFA-100 test is usually performed prior to a full platelet function study. If the PFA-100 test is within normal limits, platelet function studies are rarely of assistance.

If the PFA-100 is abnormal and the routine coagulation tests are normal, then full platelet aggregation may be required for the investigation of an inherited bleeding disorder.

Application

Platelet function is predictably abnormal after ingestion of aspirin and other NSAID and in patients with uraemia.

Platelet function may be abnormal in patients with myeloproliferative disorders, myelodysplasia and in paraproteinaemia. A PFA test may confirm platelet dysfunction. Aggregation studies are rarely contributory.

Interpretation

Pattern of aggregation and presence or absence of 'primary' or 'secondary' waves defines platelet functional disorder.

Some laboratories perform studies on whole blood instead of platelet rich plasma and the significance of the result may be somewhat different.

Confirmation and further investigation in specialised laboratory.

Reference

The British Society for Haematology BCSH Haemostasis and Thrombosis Task Force. J Clin Pathol 1988; 41: 1322-1330.

Hutton RA and Ludlam CA. J Clin Pathol 1989; 42: 858-864.