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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: Helena Laboratories PlateletWorks Kit

Plateletworks® by Helena Laboratories is actually a variety of kits used to assess patient response to different antiplatelet medications, including aspirin and clopidogrel. For aspirin-resistance, the kit includes arachidonic acid (AA) coated tubes to be utilized in an in vitro diagnostic screening test performed on whole blood for the qualitative determination of platelet inhibition by aspirin. Aspirin inhibits AA-induced platelet aggregation. The change in platelet count due to activation and aggregation of functional platelets is measured using an electronic impedance-based cell counter.
The Plateletworks methodology is an adaptation of platelet aggregometry, using a cell counter to measure total platelet count in a whole blood sample and then to redetermine the platelet count on a second sample that has been exposed to a known platelet agonist, such as AA (or ADP, if clopidogrel response is being evaluated). The agonist will stimulate those platelets that are functional to aggregate into clumps, and they will not be counted as platelets in the second sample. The difference in the platelet count between samples one and two provides a direct measurement of platelet aggregation and is reported as percent aggregation. Platelets rendered inactive or non-functional by aspirin or clopidogrel do not aggregate.
The percent platelet aggregation is then calculated:
  • From the % Aggregation/Inhibition Chart supplied in the packaged tubes
  • Using the Plateletworks Calculation Wheel
  • Using the formula below
    Baseline Platelet Count - Agonist Platelet Count x 100 = % Aggregation
    Baseline Platelet Count
Normal (positive) = >60% Aggregation
Abnormal (negative) = <60% Aggregation