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The page below is a sample from the LabCE course Antiplatelet Medication Response Testing: Aspirin and Clopidogrel. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Aspirin Response Analysis: Shear Flow Technology

The PFA-100 analyzer, produced by Siemens Healthcare Diagnostics, is used to evaluate platelet function. Platelet adhesion and aggregation are induced at a high shear rate that simulates real platelet aggregation in vivo within smaller vessels.
An anticoagulated (3.2% sodium citrate) whole blood sample is added to one of two cartridges. Each cartridge contains a membrane coated with collagen and an agonist; collagen/epinephrine (CEPI) is in one cartridge and collagen/ADP (CADP) is in the other. Platelets are activated and adhere to the membrane and cause a thrombus to form within a tiny aperature in the middle of each membrane. When the membrane is occluded with aggregated platelets, the timer stops. The time that it takes for complete occlusion to occur is called the closure time (CT) and is the measure of platelet activity. The CT is recorded and compared to reference intervals. A prolonged CT with CEPI only indicates the presence of aspirin or aspirin-like products such as non-steroidal anti-inflammatory medications. CEPI-induced CT should be prolonged when the patient is taking aspirin. If the result shows a lack of inhibition with epinephrine and collagen, aspirin resistance may be indicated. If the CT is prolonged with both the CEPI and the CADP cartridges, it suggests platelet dysfunction, and confirmatory testing would be needed.
Quality control for this instrument includes reagent QC utilized with normal patient samples each time an aggregation study is performed (according to good laboratory practice guidelines). The manufacturer recommends analyzing QC with normal patient samples with each new shipment of reagents.

The PFA-100 methodology animation available here (http://www.platelet-research.org/3/pfa.htm) is used with permission of the Platelet Research Laboratory and Siemens Healthcare Diagnostics.