A Practical Guide to Haemostasis

Platelet Function Testing: Introduction


An evaluation of patients with abnormal bleeding symptoms requires an objective assessment of the bleeding history, a physical examination, a careful drug history and followed by laboratory investigation.  

Quantitative and qualitative platelet disorders are common amongst patients with abnormal bleeding and may be clinically indistinguishable from other haemostatic disorders.  It is probable that because of the complexity of platelets and the difficulty in investigating them, that we under diagnose disorders of platelet function.

     - Laboratory tests for platelet disorders may include:
     - Assessing platelet number and size [MPV]
     - Assessing platelet morphology – blood film
     - Screening tests of platelet function e.g. Activated Clotting Time [ACT], Bleeding Time [BT] and PFA-100
     - Light Transmission Aggregometry [LTA] e.g. classical Born aggregometry
     - Impedance platelet aggregometry
     - Plateletworks - for monitoring the response of platelets to anti-platelet therapy
     - PFA-100
     - PFA-200
     - Global Thrombosis Test
     - TEG/ROTEM
     - Assessment of platelet nucleotides
     - Measurement of Thromboxane metabolites by ELISA
     - Flow cytometry e.g. to quantitate the presence or absence of platelet membrane glycoproteins
     - Mutational analysis

The aim of this section is introduce you to the complexities of investigating platelet function and to provide some help in how to investigate a patient with a suspected platelet function abnormality. 

There are some excellent reviews on the subject of platelets and these are referenced in the relevant sections.


This is not a comprehensive list of platelet function disorders but it is useful to have a scaffold that you can fit the various platelet function disorders into:

Disorder Possible Diagnoses
Abnormalities of the platelet receptors for adhesive proteins [Disorders of platelet adhesion] Bernard Soulier Syndrome [BSS]
  - BSS
  - Velo-Cardio-Facial [VCF] syndrome
Glanzmann's Thrombasthenia [GTT]
  - Congenital Afibrinogenaemia [although not a primary platelet disorder – fibrinogen is required for platelet-platelet interaction
Von Willebrand Disease
  - VWD or Platelet-type VWD
Collagen receptor defects
Abnormalities of the platelet receptors for soluble agonists [released during platelet activation] TxA2 receptor defects
α-adrenergic defects
P2Y12 receptor defects
  - Inherited deficiencies
  - Drugs e.g. Clopidogrel
Abnormalities of platelet granules Dense-granule deficiency
  - Inherited or acquired α-granule deficiency
  - Gray Platelet Syndrome
  - Quebec platelet disorder
Abnormalities of Platelet Secretion or the Signal Transduction Pathways [Impaired secretion of granule contents] Primary Secretion Defects
  - Defects in aggregation which are similar to those seen in Storage Pool Disorders [SPD] but normal granule contents and normal TxA2 generation
Defects in the agonist receptors on the surface of platelets
  - Epinephrine
  - Thromboxane
  - ADP
  - Collagen
Defects in G protein activation [defective intracellular signalling]
Abnormalities of Arachidonic Acid metabolism COX deficiency
Thromboxane synthase deficiency
Disorders of the platelet procoagulant mechanism Scott Syndrome
Platelet cytoskeletal defects MYH9-related disorders
Wiskott-Aldrich Syndrome


Click HERE to see a more comprehensive summary.