The impact of intravenous aspirin administration on platelet aspirin resistance after on-pump coronary artery bypass surgery.

Aspirin resistance continues to be a major challenge in patients after coronary artery bypass grafting (CABG). We investigated the impact of intravenous aspirin on platelet function in this clinical setting. Forty-two patients received 100 mg of oral aspirin once daily, beginning on day 1 after the operation. Between day 6 and 8 post operation one oral dose was replaced by an intravenous dose of 300 mg. Platelet function analyzer (PFA-100) closure times (CT), turbidimetric platelet aggregation (TPA) and impedance platelet aggregation (IPA) induced by arachidonic acid (AA), collagen and ADP were measured prior to and 1 h and 24 h after intravenous aspirin. Results obtained prior to the intravenous aspirin were compared with respective values from 120 healthy individuals. Despite the postoperative oral aspirin that was given once daily, ADP-induced TPA (ADPTPA) and IPA values induced by AA, ADP or collagen were significantly greater in patients than in controls, while PFA-100 CT were significantly shorter. Intravenous aspirin induced a significant reduction of platelet aggregability as measured by collagen/epinephrine (CEPI) CT, TPA and IPA induced by AA and collagen 1 h and 24 h after administration. Intravenous aspirin was not found to influence collagen/ADP (CADP) CT and IPA induced by ADP. Concomitantly, the number of patients with laboratory aspirin resistance as measured by CEPI-CT and TPA but not by IPA induced by AA or collagen dropped significantly. Agreement in the detection of aspirin responders and non-responders among platelet function tests was poor. Our findings indicate that the intravenous aspirin appears to be a promising approach for reducing laboratory aspirin resistance during the postoperative phase of CABG.

Preservation of platelet aggregation and dense granule secretion during extended storage of blood samples in the presence of a synthetic dual inhibitor of factor Xa and thrombin.

The clinical significance of platelet function tests may be limited by the use of citrate anticoagulant. We examined the influence of BAPA, a dual inhibitor of factor Xa and thrombin, on platelet responsiveness to agonists when measured between 2 and 48 h after venipuncture. Blood samples from 24 healthy individuals were anticoagulated with citrate or BAPA. Impedance platelet aggregation (IPA) and adenosine triphosphate (ATP) release induced by ADP, collagen and thrombin-receptor activating peptide (TRAP) were determined in whole blood after a storage period between 2 and 48 h after venipuncture. Citrate resulted in significantly reduced collagen or TRAP-induced IPA and ATP release when measured 32 h and 48 h after blood collection. ADP-induced IPA and ATP release in citrated blood dropped significantly between 8 and 24 h. The length of storage of BAPA-anticoagulated blood samples over 48 h had no significant influence on platelet response to collagen and TRAP. In BAPA-anticoagulated blood, ADP-induced IPA and ATP secretion in whole blood were maintained over a storage period of 32 h. No difference in ADP-induced ATP secretion in whole blood anticoagulated with citrate and BAPA was observed, but it was largely suppressed in BAPA-anticoagulated platelet rich plasma. IPA and ATP release remain stable for at least 32 h when whole blood is anticoagulated with a dual inhibitor of factor Xa and thrombin. This would allow shipment of samples for platelet function testing on the following day. Platelet secretion studies in whole blood may include platelet activation by ADP when BAPA is used as anticoagulant.

Variables influencing Multiplate(TM) whole blood impedance platelet aggregometry and turbidimetric platelet aggregation in healthy individuals.

We investigated the relationship between impedance platelet aggregometry (IPA) as measured by the Multiplate system and turbidimetric platelet aggregation (TPA) induced by ADP, arachidonic acid (AA), and collagen; blood cell counts; platelet function analyzer (PFA-100) closure times (CT), and von Willebrand factor (VWF) in 120 well-characterized healthy individuals. Pre-analytical and analytical conditions were standardized comprehensively. Analytical reliability of IPA and TPA and the influence of pre-analytical variables on assay results were also examined. IPA and TPA did not change significantly between 0.5 and 5 hours after blood collection when samples were stored at room temperature. TPA and IPA showed significantly greater intra-assay imprecision than respective TPA induced by the same agonists. Intra-individual variation did not differ significantly between IPA and TPA. The lower limits of reference range (2.5th percentiles) of AAIPA, ADPIPA and collagen IPA determined AM were 37, 20 and 40 AU, respectively. ADPIPA showed significantly lower maximum aggregation values than AAIPA and collagen IPA (P < 0.0001). There were no significant differences in any parameter between males and females. No significant differences between blood group 0 and non-0 individuals were noted with respect to IPA and TPA. IPA did not change significantly during the day. In contrast, TPA measured PM was significantly lower than corresponding values determined a.m. (p < 0.0001). CEPI-CT, CADP-CT and leukocyte counts increased significantly from a.m. to p.m. (P = 0.008 and P > 0.0001, respectively). Donors had significantly greater IPA induced by any agonist than non-donors (P-values < 0.0001, 0.0001 and 0.001, respectively), whereas TPA was not significantly different between donors and non-donors. IPA did not correlate significantly with TPA nor with PFA-100 CT. ADPIPA and collagen IPA correlated significantly with platelet count. TPA was not associated with platelet count. An inverse significant correlation was observed between TPA induced by any agonist and leukocyte count, whereas leukocyte count did not influence IPA. CEPI-CT and CADP-CT correlated significantly with VWF:CBA and with each other but not with TPA. We concluded that IPA and TPA measure different aspects of platelet function. IPA results reflect interactions between platelets, red and white cells, while TPA does not. This explains discrepancies in associations of IPA and TPA with cell counts, time of day and blood donation. The clinical significance of IPA determined using the Multiplate device remains to be determined in studies on patients with platelet dysfunction and under treatment with antiplatelet agents.

Variables influencing Platelet Function Analyzer-100 closure times in healthy individuals.

We investigated the relationship between platelet function analyzer (PFA-100) closure times (CT) and bleeding time (BT), platelet aggregation (PA) induced by ADP, arachidonic acid, and collagen, blood cell counts, and von Willebrand factor (VWF) in 120 well-characterised healthy individuals. Pre-analytical and analytical conditions were standardised comprehensively. In a substantial number of cases the differences between duplicate measurements exceeded 15%. The reference range (5th and 95th percentiles) for CT with the collagen/epinephrine (CEPI) and the collagen/ADP (CADP) cartridge was 93-223 s and 64-117 s respectively. Re-examination of 11 individuals with CEPI-CT above the 95th percentile revealed considerable batch-to-batch variation of CEPI-CT. Males had significantly longer CADP than females (P = 0.002). CEPI and CADP-CT measured pm were significantly longer than corresponding values determined am (P = 0.003 and P < 0.0001 respectively). Blood group O was associated with greater CEPI and CADP-CT and lower VWF levels compared with non-O blood groups (P = 0.008, P = 0.0003 and P < 0.0001 respectively). Linear regression analysis revealed association between CEPI-CT, CADP-CT and VWF (P < 0.0001), but no relationship was found between CT and BT or between CT and PA. We conclude that VWF plasma levels modulate PFA-100 CT to a greater extent than platelet function. Establishment of reliable reference ranges and careful standardisation of pre-analytical and analytical conditions is a prerequisite for obtaining reliable PFA-100 results. Duplicate measurements are necessary.