Here is a question about the bleeding time from Sue Hillyard:
I was recently asked to perform a bleeding time on a patient who was on Plavix. The reason for this was that the “PFA is insensitive to Plavix, the bleeding time is more sensitive.” Is this technically correct? If so, why?
Hi, Sue. You can monitor for Plavix (clopidogrel) efficacy using the bleeding time,Accumetrics VerifyNow, and the reference method, platelet aggregometry. The bleeding time is not reproducible and has been largely discontinued. The PFA-100, according toMueller T, Haltmayer M, Poelz W, Haidinger D. Monitoring aspirin 100 mg and clopidogrel 75 mg therapy with the PFA-100 device in patients with peripheral arterial disease. Vasc Endovascular Surg 2003;37:117-23, is sensitive to aspirin but not Plavix, and Siemens, which manufactures and distributes the PFA-100, makes no claim for Plavix monitoring. Accumetrics has an FDA-approved system for monitoring Plavix. My personal preference, if available, is whole blood platelet aggregometry, which is easy to perform and reproducible. I hope this is helpful. Geo.
From Jennifer Wege, We have a nurse practit
From Jennifer Wege, We have a nurse practitioner who insists we use the ADP closure time from our PFA-100 to assess her cardiac patients for Plavix resistance. She believes that a high ADP closure time means her patient is responding to Plavix therapy, and a normal ADP closure time means her patient is resistant. Is there any literature out there that supports this? We have been putting a big disclaimer on our lab reports that Siemens does not recommend using their platelet function test in this manner.
Jennifer, the Siemens PFA-100 Platelet Function Analyzer Collagen/ADP cartridge is cleared only to screen for platelet activity defects and von Willebrand disease. Siemens states that the cartridge is not cleared for measuring Plavix response. To my knowledge, platelet aggregometry, the Multiplate Analyzer (DiaPharma) and the Accumetrics VerifyNow PRUTest P2Y12 are the three methods cleared by the US FDA to measure clopidogrel (Plavix) and prasugrel (Effient) efficacy. I’ve sent your note on to some of our consultants for further verification.