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Thromb Haemost 2012; 107(03): 538-544
DOI: 10.1160/TH11-09-0623
Platelets and Blood Cells
Schattauer GmbH

Vasodilator-stimulated phosphoprotein-phosphorylation assay in patients on clopidogrel: Does standardisation matter?

Matthias K. Freynhofer
1   3rd Medical Department, Cardiology and Emergency Medicine, Wilhelminenhospital, Vienna, Austria
2   Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna, Austria
,
Veronika Bruno
1   3rd Medical Department, Cardiology and Emergency Medicine, Wilhelminenhospital, Vienna, Austria
3   Department of Obstetrics and Gynaecology, Wilhelminenhospital, Vienna, Austria
,
Martin Willheim
4   Department of Laboratory Medicine, Wilhelminenhospital, Vienna, Austria
,
Wolfgang Hübl
4   Department of Laboratory Medicine, Wilhelminenhospital, Vienna, Austria
,
Johann Wojta
2   Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna, Austria
5   Department of Cardiology, Medical University of Vienna, Vienna, Austria
,
Kurt Huber
1   3rd Medical Department, Cardiology and Emergency Medicine, Wilhelminenhospital, Vienna, Austria
2   Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna, Austria
› Author Affiliations
Further Information

Publication History

Received: 11 September 2011

Accepted after major revision: 01 January 2011

Publication Date:
22 November 2017 (online)

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Summary

The vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P) flow-cytometric assay is mainly used in clinical trials to measure thienopyridine effects. However, there are remarkable differences in the reported optimal cut-offs, ranging from 48–61% platelet reactivity index (PRI). We therefore investigated whether a lack of standardisation might explain the differences in the cut-offs. We measured VASP-P in 62 individuals. PRI was calculated using the mean, geometric mean and median fluorescence intensities (FI). Stability of the blood-samples (time-to-assay, 0–2 days) and stability of the processed samples (0–120 minutes) within the recommended time-span were tested. Time-to-assay significantly influenced the PRI (p<0.001): the PRI from mean FI after two days was lower compared to values on day 1 (52 ± 22.9 vs. 57.7 ± 24.1, p<0.001). The PRI from the geometric mean FI after two days was lower compared to day 0 as well as day 1 (51.3 ± 23 vs. 58.2 ± 24.2 and vs. 59.1 ± 23.7, both p<0.001). The PRI from median FI was stable over time (day 0: 59.1 ± 25%, day 1: 59.7 ± 24.1% and day 2: 56.4 ± 23.9%, all p=ns). Furthermore, the lag time of the processed samples significantly altered the PRI (all p<0.001) with a maximum difference for PRI based on geometric mean FI after 90 minutes compared to baseline (Δ=3.92%PRI, p<0.001). The differences in the reported cut-offs might be explained by a lack of standardisation. More precise standardisation is inevitable, as the PRI significantly depends on the method of calculation, the time-to-assay as well as on the lag time after processing. Tolerably stable results were obtained for the PRI from the median FI.

Keywords

Clopidogrel - thienopyridines - VASP-P assay - platelets
 

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