A question from my colleague and our former graduate student, Rebecca Jones:
Hey, George. When patients are sent to general surgery or to have a stent put in, how much inhibition of platelets is acceptable for procedures to be performed? We have been doing a calculation giving surgeons percent inhibition, but are being asked to switch to the PRU system instead. Thanks so much!
Hi, Rebecca, it is good to hear from you. I presume from your message that you plan to be using the VerifyNow P2Y12 cartridge for monitoring Plavix before and after surgery and reporting the result in PRUs. This may be an acceptable substitute for platelet aggregometry provided your surgeons understand the result is qualitative, indicating only that the assay is positive or negative for Plavix’s antiplatelet effect. They should not interpret either aggregometry results or the PRU results as indicating a degree of antiplatelet effect, they should just think “all or nothing.” I don’t recommend a % inhibition calculation.
The guidelines for management of aspirin or plavix at the time of surgery are available from Douketis JD, Alex C. Spyropoulos AC, Spencer FA , et al. Perioperative Management of Antithrombotic Therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines CHEST 2012; 141:e326S–e350S.
Their recommendation is “In patients who are receiving ASA and require CABG surgery, we suggest continuing ASA around the time of surgery instead of stopping ASA 7 to 10 days before surgery (Grade 2C). In patients who are receiving dual antiplatelet drug therapy and require CABG surgery, we suggest continuing ASA around the time of surgery and stopping clopidogrel/prasugrel 5 days before surgery instead of continuing dual antiplatelet therapy around the time of surgery (Grade 2C).”
This is a little different from the 2008 Chest guidelines, which recommended discontinuing aspirin and plavix 7-10 days before surgery, and the current grade 2C level of recommendation is weak, so your surgeons are justified in making their own interpretation. However, whether you use the 2008 and 2012 guidelines, Plavix should be discontinued at least five days before surgery. I hope this helps. Geo.
I just read an interesting article by Voisin S et al: Th
I just read an interesting article by Voisin S et al: Thromb Haemost 2011;106:227-228, titled “Are P2Y12 reaction unit (PRU) and % inhibition index equivalent for the expression of P2Y12 inhibition by the VerifyNow assay? role of haematocrit and haemoglobin levels?” It may contradict the issue of reporting PRUs vs %inhibition. In this study the results showed that PRU significantly decreases with increasing HCT/HGB, whereas % inhibition does not, due to a parallel change in PRU and iso-(thrombin receptor activation peptide) TRAP baseline value. PRU and % inhibition index are not equivalent for the definition of high on-treatment platelet reactivity because of their different sensitivities to HCT/HGB. In their study a PRU value of 23% corresponded to 27% inhibition at T1 and 35% inhibition at T2 respectively. PRUs have been the preferred mode of expression in a lot of clinical trials, however the authors of this one noted in contrast with PRU the % inhibition is independent of haematological variables. They stated that a clinical trial should be performed to determine if PRU or % inhibition is truly predictive of clinical events.
Dave McGlasson
59th Clinical Research Division
LAFB, TX