Evaluation of Residual Platelet Reactivity in Patients Treated with Aspirin and or Clopidogrel: Comparison of Results Obtained On Multiplate^®, PFA-100^TM and Classical Light Transmission Aggregometry.

Ninety-three controls, healthy volunteers or patients without intake of AT or other drugs or pathology impairing platelet functions and 182 consecutive patients on AT were studied. Among patients, 61 received Aspirin 100mg (group A), 36 Clopidogrel 75mg (group C) and 85 the association of the two drugs. Among these 85 patients, 58 received continuously Aspirin 75mg and Clopidogrel 75mg (group AC) and 27 received a loading dose for both drugs before coronarography (group LAC).

Venous blood samples were obtained on Becton Dickinson vacutainer containing citrate 0.129M.

Multiplate^® measures change in electrical resistance as arbitrary aggregation units (AU) over time. Aggregation is quantified as AU and area under the curve (AUC) of AU.min. On LTA, aggregation was quantified according to manufacturer's recommendations as AUC. “Resistance” to Aspirin or Aspirin RPR was determined on Multiplate^® (M) using arachidonic acid at 0.5 mM (ASPITEST), in LTA with arachidonic acid at 1 mM (AA-LTA) and on PFA-100^TM using the cartridge with membrane coated with epinephrine (PFA-EPI). In the same way, “resistance” to Clopidogrel was determined on M using ADP at 6.4 μM (ADPTEST), in LTA with the presence of ADP at 10 μM (ADP-LTA) and occlusion time on PFA-100^TM using cartridge with membrane coated with ADP (PFA-ADP).

All patients were tested on M, 169 on PFA-100^TM and 37 with LTA. Significant correlations (p<.0001) were observed between ASPITEST and AA-LTA (r = .771), ASPITEST and PFA-EPI (r = -.42), AA-LTA and PFA-EPI (r = -.47), ADPTEST and ADP-LTA (r = .6) ADPTEST and PFA-ADP (r = -.39) and ADP-LTA and PFA-ADP (r = -.56).

To define RPR on M and LTA, cut-off values (5^th percentile) were determined from controls for each inducer. Treated patients presenting reactivity higher than the threshold value were considered as ‘resistant’. For PFA-100^TM, results of patients under cut-off point defined by the manufacturer were considered as ‘resistant’.

The frequency of “resistant” patients according to the different platelet functions tests was: a) for Aspirin: 10% on M, 4.5% with LTA and 32.8% with PFA-EPI. b) for Clopidogrel 23.1% on M 16.1% with LTA and 54.5% with PFA-ADP.

A good agreement was found between ASPITEST and AA-LTA and between ADPTEST and ADP-LTA (respectively 92% and 88.7%). On the other hand, results on comparison between ASPITEST and PFA-EPI and LTA and PFA-EPI were respectively 70% and 72.6%. Results for ADPTEST and PFA-ADP were 69% and 72.3% for ADP-LTA and PFA-ADP.

A significant gradation of mean AUC was observed using ASPITEST on M between all groups of subjects: controls (mean = 494±176); group A (mean = 214±186); group C (mean = 310±198); group AC (mean = 118±109); group LAC (mean = 74±45). Similar results are obtained with LTA and on PFA-100^TM (except for the group C, Clopidogrel alone). Thus, a potentiating effect of Aspirin by the association with Clopidogrel may be postulated in this study.

Using ADPTEST to assess the treatment response by clopidogrel, mean AUC were significantly lower for all group of patients with Clopidogrel than for controls. No gradient has been observed. Mean AUC of patients with Aspirin alone was similar to controls.

In conclusion, our results confirm that Multiplate^® is more effective than PFA-100^TM in monitoring patients on AT. The good agreement between Multiplate^® and LTA could lead to use the Multiplate^® in first intention to detect RPR in these patients. Furthermore the easiness of Multiplate^® use may contribute to development of new studies on biological activities of AT.

No relevant conflicts of interest to declare.