Determination of Aspirin Responsiveness by Use of Whole Blood Platelet Aggregometry

Abstract

Background: Insufficient platelet inhibition is associated with an increased cardiovascular risk in up to 30% of patients taking regular doses of aspirin. We describe an assay to study aspirin responsiveness. Methods: We performed impedance aggregometry on diluted whole blood with 1 mg/L collagen and 0.5 mmol/L arachidonic acid (AA). We measured thromboxane B 2 (TXB 2 ) by RIA. We examined 66 healthy control individuals, 144 aspirin users with stable coronary artery disease (CAD), and 245 CAD patients treated with aspirin and clopidogrel. Nonresponsive samples were incubated with excess DL-lysinmonoacetylsalicylic acid. Results: Assay imprecision (CV) was 9.8% and 8.2% at mean (SD) 6-min impedance of 13.7 (2.8) ⍀ and 13.6 (2.3) ⍀ for collagen and AA, respectively. Collagen induced stronger aggregation (P ‫؍‬ 0.0199) in women [n ‫؍‬ 28, 14.6 (2.4) ⍀] than in men [n ‫؍‬ 38, 13.1 (2.9) ⍀], even after sample incubation with 0.1 mmol/L acetylsalicylic acid (ASA) or 1 mol/L terbogrel, a combined inhibitor of thromboxane synthase and receptors. The sex association persisted in aspirin users, but not if clopidogrel was also taken. A 6-min impedance >8 ⍀ with collagen (mean ؊ 2 SD of the controls) was taken as evidence of nonresponsiveness, particularly if incubation with ASA did not inhibit aggregation further (>2 ⍀). Compared with AA, collagen identified more nonresponsive samples among aspirin users (15%) and CAD patients who also received clopidogrel (10%). Incubation with ASA improved inhibition of aggregation in 70% of samples and consistently reduced TXB 2 formation during aggregation.

The prognostic utility of tests of platelet function for the detection of ‘aspirin resistance’ in patients with established cardiovascular or cerebrovascular disease: a systematic review and economic evaluation

“…Criteria similar to ones cited (references given [226][227][228][229][230] No details (but quality control procedures described) A predetermined threshold percentage (for platelet aggregation) was given in four studies. 99,117,128,186 Thresholds were > 1 Ω 99 at least 50% platelet response; 117 and > 10 Ω in response to 1 μg/ml of collagen, > 50% of the response to 5 μg/ml of collagen and/or > 6 Ω to 0.5 mM arachidonic acid.…”

Dual Antiplatelet Drug Resistance Is a Risk Factor for Cardiovascular Events after Percutaneous Coronary Intervention

“…We performed whole-blood impedance aggregometry the day after clopidogrel loading using described protocols for the CA560 lumi-aggregometer (ChronoLog) (7,8 ). In brief, aggregation was determined by measuring the increase in impedance (⍀) between a pair of metal electrodes immersed in whole blood diluted 1:1 with NaCl (9 g/L).…”

“…Such studies are difficult to perform because standardized assays for aggregometry are lacking (6 ). Recently, we validated assays using impedance aggregometry to study the aggregation responses to ASA and clopidogrel (7,8 ). We enhanced the specificity of these assays by in vitro incubation of blood samples with ASA or methyl-S-adenosine monophos-phate (Me-S-AMP), a selective ADP-(P2Y 12 )-receptor blocker.…”

“…This information is helpful for patient management because platelet inhibition can be improved by increased doses of clopidogrel and/or ASA in patients with a pharmacokinetic resistance. In comparison, pharmacodynamic resistance is less frequent (with a prevalence of approximately 2%) but requires switching to an alternative antiplatelet drug (7,8 ).…”

Design Considerations for a Microfluidic Device to Quantify the Platelet Adhesion to Collagen at Physiological Shear Rates

“…In individuals with cardiovascular disease, excess platelet adhesion and aggregation can result in heart attack and stroke. There are several techniques available that can measure platelet adhesion or aggregation in vitro, the most widely used being aggregometry 5,12,19,21 which assess platelet-platelet interactions. However, these devices do not provide an accurate mechanical environment which is essential for proper platelet function nor do they allow for the assessment of platelet adhesion to a thrombogenic surface in the presence of physiologically relevant fluid mechanical forces.…”