Here’s additional follow-up to Heather DeVries’s February 9 whole blood lumiaggregometry discussion, which attracted comments from Bob Gosselin, Dave McGlasson, and Drs. Catherine Hayward and Emmanuel Favaloro. Dr. Favaloro references the effort to clean cuvettes and probes in the whole blood system, so I want to reassure Heather that these components are now disposable. I’m not sure why it would seem that cleaning whole blood devices is any more difficult than cleaning PRP devices, perhaps the residue is just more visible?
Hundreds of projects have addressed aspirin resistance (aspirin non-responders) and clopidogrel (Plavix) dosing, and many correlate non-response to adverse outcomes–arterial and venous thrombosis. Companies have sprung up to provide instruments and methods that detect anti-platelet non-response, and Warren Varden at UAB tells me the majority of their 55–80 monthly aggs are ordered to check for non-response, especially to clopidogrel. Non-responder Plavix patient doses are raised to 150 mg/day. However, as Dr. Favaloro states, few reliable outcomes studies record improvements in efficacy associated with dose adjustment. Further, McGlasson DL, Fritsma GA. Comparison of four laboratory methods to assess aspirin sensitivity. Blood Coag Fibrinolysis 2008; 19 reports that although each method detected a percentage of aspirin non-responders, the four methods detected separate sets of non-responding subjects; there was no cross-platform correlation. We showed that non-responder classification was technique-dependent. So, as Dr. Hayward says, your choice of methodology, for instance Accriva VerifyNow, Siemens PFA 100/200, Multiplate, whole blood lumiaggregometry, light transmittance (optical) aggregometry, or even the now obsolete bleeding time, may be a matter of faith.
With this as background, I continue to support whole blood lumiaggregometry on the basis of superior specimen management, the more natural milieu, and a clear secretion indication in response to thrombin, TRAP, and AA.
Warren’s colleague at UAB add
Warren’s colleague at UAB add that when the platelet count is less than 100,000/uL, it is necessary to add a reduced volume of saline to achieve valid aggregation patterns., down to as little as 100 uL. She continues that If the platelet count is so low that you don’t want to add saline it’s not worth trying. As with optical aggregometry, you’re not going to be able to tell the difference between a platelet disorder and thrombocytopenia. Further, making up arachidonic acid isn’t all that hard. It’s just pipetting and 5 minutes of vortexing.