Platelets

• produced from megakaryocytes

• circulate for 7-10 days

Structure

• Membrane - phosphatidyl serine

• Skeleton

• Granules - alpha, dense

Functions

1. adhesion

2. activation

3. shape change

4. secretion

5. aggregation

Tests

• FBC

Platelet aggregation tests

• platelet rich plasma in an optical sensor - if aggregate then more light passes through plasma

• Test by addition of

  • ADP

  • adrenaline

  • collagen

  • arachidonic acid

  • Ristocetin

• Results

  • e.g. in Glanzmans then only Ristocetin causes aggregation, in Bernard-Soulier Ristocetin is the only one not to cause aggregation

Disorders

Causes of an elevated platelet count (thrombocythaemia)

Primary

• Essential thrombocythaemia

• As part of another myeloproliferative disorder

  • chronic myeloid leukaemia

  • polycythaemia rubra vera

Secondary / Reactive

• Iron deficiency

• Haemorrhage

• Severe haemolysis

• Trauma, post-op

• Infection

• Inflammation

• Malignancy

• Hyposplenism

Reduced platelet levels / function

Classification

• functional  or quantitative (Thrombocytopenia)

• congenital or acquired

Inherited functional disorders

• Glanzman's thrombasthenia

• Bernard-Soulier syndrome

• Storage Pool Disease

  • dense gransules

  • low platelet ADP

Acquired disorders

• low-dose aspirin

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