Platelet function tests

What it measures

Assess how well platelets stick and clump in response to agonists such as ADP, collagen, epinephrine, arachidonic acid and ristocetin. Used in unexplained bleeding and to check antiplatelet drug effect.

Specimen and preparation

• Specimen: Citrated whole blood (3.2%), tested within 4 h at room temperature
• Tube: Light_blue top
• Preparation: Avoid aspirin, NSAIDs and other antiplatelet drugs for 7–10 days unless testing drug effect. Do not refrigerate or send by pneumatic tube.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Aspirin (absent arachidonic acid response)
• Clopidogrel and other P2Y12 inhibitors (reduced ADP response)
• Glanzmann thrombasthenia
• Bernard-Soulier syndrome (absent ristocetin response)
• von Willebrand disease
• Uremia, storage pool disorders

Method

Light transmission aggregometry on platelet-rich plasma; PFA-100 closure time; whole-blood impedance

Good to know

Low platelet count (<100 ×10⁹/L) or hematocrit (<30%) invalidates PFA-100 results. Values vary by lab and cartridge lot.

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