Application of the Cone and Plate(let) Analyzer as a Point-of-Care Method for Monitoring Anti-Platelet Therapy.

Platelet anti-aggregants play a major role in the treatment of cardiovascular disorders. Recently it has been suggested that a significant proportion of patients fail to respond to these agents according to different testing methods. We have developed a new method for evaluating the response to platelet anti-aggregants, the modified Cone and Plate(let) Analyzer (CPA) test. The method is based on the observation that pre-activation of platelets by an agonist will result in reduced platelet deposition on a polystyrene surface under arterial flow conditions (the phenomenon of platelet adhesion refractoriness). In vitro studies demonstrated that the basic platelet adhesion (surface coverage, SC 12.3±6.8%) was significantly reduced in response to pre-incubation of the sample (for 1 min) with arachidonic acid (AA, SC 2.1±1.5%), adenine diphosphate (ADP, SC 1.3±0.6%) and epinephrine (EPI, 2.9±0.9%). This effect was selectively inhibited by aspirin (for the response to AA, SC 8.1±3.8%), and by 2-Methylthio-AMP triethylammonium (2-MeSAMP), a selective inhibitor of P2Y12 (for the response to ADP, SC 4.8±2.0%), p<0.001. The potential application of this method for monitoring the effect of aspirin therapy (daily doses of 100, 300 and 500 mg), among 20 healthy volunteers was investigated in comparison to turbidimetric aggregometer. All volunteers responded to aspirin in the three doses according to the aggregometer test (reduced max. aggregation from 88±8% to 12.4±7%), with no evidence for a dose response manner in this dose range. Basic platelet adhesion as tested by the CPA (SC 9.8±2.2%), was unaffected by aspirin in the three tested doses. However, the response to pre-incubation with AA was significantly inhibited by aspirin in all patients (SC of 0.6±0.3% before aspirin therapy and 3.5±1.3%, 4.4±1.7%, and 4.1±2.0% following therapy with 100, 200 and 500 mg aspirin per day, respectively, p<0.001 for all doses), again with no dose response effect. This effect was specific for AA, since no difference in SC was observed when ADP was used as an agonist. A significant correlation between the effect of aspirin as tested by the modified CPA and by the turbidimetric aggregometer using AA as an agonist (R²=0.55) was observed. In conclusion, the CPA was found useful point-of-care method for testing the response of platelets to aggregating agonists as well as for monitoring the effect of anti-platelet drugs.