Evaluation of the platelet count drop method for assessment of platelet function in comparison with "gold standard" light transmission aggregometry.
BACKGROUND
Hyporesponsiveness to antiplatelet agents has been linked to an increased risk of major adverse cardiovascular events. However, light transmission aggregometry (LTA), the gold standard methodology for assessing platelet function, requires expertise and is labour-intensive, which render its use in clinical settings impractical. We assessed whether platelet count drop (PCD), a technique widely available in any haematology laboratory, could replace LTA in testing for inhibition of platelet aggregation induced by antiplatelet agents.


METHODS
One hundred and sixty-one coronary artery disease patients taking aspirin alone and 91 patients taking a combination of aspirin and clopidogrel were enrolled. Platelet aggregation was measured by LTA and PCD stimulated with 1.6 mM of arachidonic acid (AA) for aspirin and 5 and 20 microM of adenosine diphosphate (ADP) for clopidogrel.


RESULTS
Correlation between AA-induced LTA and PCD was nonexistent (r=-0.043, p=0.587), while correlation between ADP-induced LTA and PCD was low (r=0.374, p<0.0001 for ADP 5 microM and r=0.402, p<0001 for ADP 20 microM ). PCD, whether stimulated with AA or ADP, overestimated platelet aggregation as assessed by LTA, by 13-18%. The wide 95% limits of agreement suggest that the assays can disagree significantly in individual patients.


CONCLUSIONS
Although the PCD method is widely available in non-specialized laboratories, our results demonstrate that there is poor correlation with the current gold standard, i.e. LTA. Thus, PCD should not be used in replacement of LTA to assess antiplatelet responsiveness.
Lordkipanidzé
Marie
M
Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada.
Pharand
Chantal
C
Schampaert
Erick
E
Palisaitis
Donald A
DA
Diodati
Jean G
JG
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000368:Aged; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000008:administration & dosage; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D000077144:Clopidogrel; D003324:Coronary Artery Disease / Q000097:blood / Q000188:drug therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D010976:Platelet Count; D010979:Platelet Function Tests / Q000379:methods*; D015203:Reproducibility of Results; D013988:Ticlopidine / Q000008:administration & dosage / Q000031:analogs & derivatives
D010975:Platelet Aggregation Inhibitors; D016718:Arachidonic Acid; D000244:Adenosine Diphosphate; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin