Platelet aggregation is dependent on platelet count in patients with coronary artery disease.

INTRODUCTION: Platelet function testing in whole blood is widely used to evaluate the effect of antiplatelet agents, but it is not known whether results are affected by whole blood parameters. This study investigated the importance of platelet count, haematocrit, red blood cells (RBC), and white blood cells in whole blood platelet aggregometry.

MATERIALS AND METHODS: We included 417 patients with coronary artery disease on aspirin mono-therapy and 21 aspirin-naïve healthy individuals. Blood sampling was performed one hour after aspirin ingestion. The antiplatelet effect of aspirin was evaluated using the VerifyNow® Aspirin assay and multiple electrode aggregometry (MEA, Multiplate®) induced by collagen (1.0 μg/mL) and arachidonic acid (1.0 or 0.75 mmol/L). Measurements of whole blood parameters were performed to evaluate the three major cell lines in circulating blood.

RESULTS: In patients, platelet count correlated significantly with platelet aggregation (MEA(collagen), p<0.0001; MEA(arachidonic acid), p<0.0001; VerifyNow®, p=0.03). Haematocrit and RBC correlated inversely with MEA induced by collagen (p(haematocrit)<0.001; p(RBC)=0.07) and with VerifyNow® (p(haematocrit)<0.0001; p(RBC)<0.0001), but not with MEA induced by arachidonic acid (p(haematocrit)=1; p(RBC)=0.87). White blood cells correlated significantly with platelet aggregation (MEA(collagen), p<0.001; MEA(arachidonic acid), p<0.0001; VerifyNow®, p=0.05). Similar associations were observed in aspirin-naïve healthy individuals.

CONCLUSIONS: Whole blood aggregometry is dependent on all major cell lines in whole blood. Importantly, platelet aggregation is significantly associated with platelet count even within the normal range.