Here is another note from Dr. James Quesenberry, St. Lukes Laboratory, Sioux City, Iowa regarding point-of-care platelet function testing using the Siemens PFA-100. His comments…
This is a test that we don’t do often but is a pain in our sides. We have always required a path interpretation, usually the patient has multiple medical problems and is on multiple meds. We get the patient med list and the list that interferes with the PFA which is long, and usually the patient is on one of the non-ASA non-NSAID meds. Do all these meds truly interfere with the PFA and therefore the test, which is already probably of no value in the situations ordered therefore become completely invalid? Is there an updated list out there? Is this effect of the non-antiplatelet drugs or is this purely an in vitro effect, indicating nothing real about the patient’s platelet function in vivo? Thanks George.
Hello, Dr. Quesenberry. You sent this question on October 4, 2017, and I referred it to acquaintances who represent Siemens, the PFA-100 distributor. I’ve received no response as of October 13. I’ll offer a few comments and await follow-up from my PFA-100 experts.
The PFA-100 is the most commonly employed point-of-care platelet function testing instrument. Its USA competitors are dedicated to measuring aspirin, NSAIDs, glycoprotein inhibitors, and clopidogrel efficacy, but are not indicated as screening tests for platelet function disorders. Testing for von Willebrand disease and platelet disorder research are the PFA-100’s only approved applications. Aspirin, NSAIDs, clopidogrel, and several additional drugs interfere with VWD testing, and the PFA‘s results are affected by hematocrit, platelet count, and specimen collection variants. Additionally, all the point-of-care instruments generate CV% results in excess of 20%, thus reproducibility can be an issue.
The ISTH article limiting the PFA-100 tp VWD and research is Hayward CP, Harrison P, Cattaneo M, Ortel TL, Rao AK. Platelet Physiology Subcommittee of the Scientific ad Standardization Committee of the International Society on Thromobosis and Haemostasis. Platelet function analyzer (PFA-100 closure time in the evaluation of platelet disorders and platelet function. J Thormb Haemost 2006:4:312–9.
I think I would concur that
I think I would concur that the PFA-100/200 be best left to VWD and maybe research. The PFA-100/200 is pretty sensitive to aspirin, but that is good and bad depending on what you are using the instrument for. The PFA is variably sensitive to other anti-platelet drugs, with effects potentially seen or missed depending on the other variables to which the PFA is sensitive (platelet count/activity, HCT, VWF level/activity). An excellent synopsis has recently been published: Favaloro EJ. Clinical utility of closure times using the platelet function analyzer-100/200. Am J Hematol. 2017;92:398–404. The PFA is an excellent negative predictor for significant VWD–a normal PFA will exclude significant VWD. See also: Favaloro EJ. The Platelet Function Analyser (PFA)-100 and von Willebrand disease: a story well over 16 years in the making. Haemophilia. 2015 ;21:642–5.