Major hindrances of impedance aggregometry are caused by limited storage time and the requirement of ex vivo anticoagulation. Data on the influence of different anticoagulants and storage conditions are rare and incomplete. This study has systematically examined the influence of six different anticoagulants (sodium and lithium heparin, 20 µg/mL and 45 µg/mL r-hirudin, benzylsulfonyl-D-Arg-Pro-4-amidinobenzylamide (BAPA), and citrate) on the results of Adenosine 5'-diphosphate (ADP) and arachidonic acid (AA) induced measurements using multiple-electrode impedance aggregometer (MEA). Measurements were carried out in a time frame of 0 min up to 48 h after blood withdrawal. In addition, the influence of storage temperatures of 4°C and 37°C was evaluated. Results of ADP-induced tests significantly varied within the first 30 min in all tested anticoagulants, in citrated blood even within the first 60 min. They remained stable up to 2 h in 20 µg/mL r-hirudin and BAPA, 4 h in citrate, 8 h in 45 µg/mL r-hirudin, and lithium heparin and up to a maximum of 12 h in sodium heparin anticoagulated blood. The analysis of AA-induced tests revealed no significantly different results up to 6 h when BAPA was used, 8 h in lithium heparin, 20 µg/mL r-hirudin and citrate, 12 h in 45 µg/mL r-hirudin, and even 24 h in sodium heparin-anticoagulated samples. A storage temperature of either 4°C or 37°C in contrast to room temperature had a negative influence on the stability of results. In conclusion, sodium heparin and 45 µg/mL r-hirudin as anticoagulants guarantee the longest storage time for impedance aggregometry.

The cytochrome P450 (CYP) isoenzymes are essential for the metabolic activation of the prodrug prasugrel. Little is known about the impact of polymorphism of these isoenzymes on the prevalence of prasugrel low responsiveness (PLR) in patients with coronary artery disease. We investigated the frequency of PLR and the question whether PLR is associated with decreased/non-function polymorphisms of the CYP isoenzymes (2C9*2, 2C9*3, 2C19*2, 2C19*3, and 2B6*6). Our study included 355 patients who underwent percutaneous coronary stenting. The patients were initially treated with either prasugrel (n=90; 60/10 mg: loading/daily maintenance dose) or 600/75 mg clopidogrel hydrogensulfate (n=265) in combination with 500/100 mg acetylsalicylic acid (ASA). Platelet function was tested by impedance aggregometry 48 hours after taking the loading dose. Prasugrel achieved on the average significantly higher levels of platelet inhibition as compared to clopidogrel (mean 27.3 U vs 41.2 U). The frequencies of low response for prasugrel, clopidogrel and ASA were 9.8%, 35.1% and 14.9%, respectively. We identified only body mass index to be associated with PLR. PLR was not caused by a loss of ADP P2Y12-receptor function. Half of the patients with PLR were carriers of the reduced-function allele CYP2B6*6, and 41.7% had the genetic variant CYP2C9*2. The allele CYP2C9*3 was detected in three patients with PLR (25%) and two patients with PLR (16.7%) carried the gene variant CYP2C19*2. In conclusion, the rate of low responders was significantly lower among patients treated with prasugrel than with clopidogrel. PLR are more often carriers of CYP2C9*2 (50% in PLR) than when compared to the prevalence described in literature. Also, there is a trend to an increased frequency of CYP2B6*6 in PLR. In conclusion, CYP2B6 and CYP2C9 polymorphisms seem to be associated with prasugrel low-response.