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Figure 2 Laboratory Assessment of Clopidogrel Responsiveness

Adenosine diphosphate (ADP) stimulates 2 distinct receptors (P2Y₁ and P2Y₁₂) that are linked to specific signaling pathways (dashed arrows). Response can be measured by: (A) receptor reactivity; intracellular signaling downstream from the P2Y₁₂ receptor is measured by flow cytometry that assesses phosphorylation of vasodilator-stimulated phosphoprotein (VASP) with monoclonal antibodies (Y); the P2Y₁₂ is coupled by a G_i protein to adenylyl cyclase; PKA = protein kinase A; (B) activation-dependent receptor expression (active glycoprotein [GP] IIb/IIIa and P-selectin) identified by monoclonal antibodies (Y) with flow cytometry; (C) aggregation determined by light transmittance aggregometry (LTA), aggregation of platelets with fibrinogen-coated beads (VerifyNow), or measuring the contribution of platelet aggregation to total platelet–fibrin clot strength by thrombelastography.

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