Has anyone here been assessing platelet function assays for their cardiac patients and other patient populations of late?

Our cardiac dept. and pathologists are considering going to a point-of-care instrument or perhaps evaluating a turbidimetric analyzer for platelet function in patients receiving clopidogrel (an ADP agonist), and/or for monitoring platelet glycoprotein IIb/IIIa activity

as affected by the meds abciximab or eptifibatide.

I don't believe there's much interest in assessing platelet function in patients with von Willebrand's or those of the rarer hereditary platelet disorders, rather just in those taking therapeutic drugs and undergoing procedures where they might require platelet transfusions and other coag factor replacement.

Have done some extensive reading on the various assays and instruments, but am interested in knowing what others have evaluated and are using. From what I understand, the PFA-100 (sysmex and dade) is not FDA-approved (no medicare reimbursement?), but there are several instruments out there (Chrono-log and Accumetrics), and their various evaluations look promising.

Normally, this sort of item is the province of the coagulation/hemo dept. but many transfusion services/blood banks have a closer relationship with the cardiac people so this assay might fall into our lap.

:coffeecup

Coagulation has always been a part of our Blood Bank area. We've been using a Dade PFA for a number of years. As our cardiac surgeons have changed over the years so, too, has the "need" for evaluating platelet functions. The Dade information on the PFA states -- and this is coming from memory at home -- something along the lines that the insturment is only rated for inherited disorders and aspirin and is not approved for monitoring the effects of these new drugs.

We have had a recent case of a patient being resistant to (if memory serves) clopidogrel. I know our path spoke with one of our PharmDs about it and the PharmD had not heard of such a thing before. But he found a reference for it. This was atypical. In our experience with patients on these medications the results are abnormal. How are your cardiac docs planning on using this information? Do they really need to know how abnormal "abnormal" is? Will the patient go to cardiac surgery based on a specific cut off for abnormal platelet function? Or will x mean one platelet apheresis unit but a value of y means two platelet aperesis units?

Hope this helps some,

Randall D. Williams MT(ASCP)BB

Mercy Medical Center - Sioux City

The discussion on platelet function assays is still very preliminary at my facility, (i.e. haven't heard of any input from the cardiac folks), but I suspect that several scenarios both within the cardiac dept. and outside it would make such an instrument very useful.

#1 Something that's geared toward determining both the baseline of platelet inhibition and inhibition after a patient receives loading doses of inhibitors (abcixmab for e.g.) and a bolus of heparin for PCI procedures and CAGBs is more along the line of what's in store. (Cath lab and cardiac suite)

#2 Also, the concern for us as a transfusion service with a limited commodity (platelets) is determining to what degree a patient's platelets have been inactivated when they suddenly need a cardiac procedure while on plavix (i.e. do we really need to transfuse someone with platelets who has a 300k count just because they took plavix and the doc is skittish).

#3 Also, a POC instrument for the ED to get a baseline on folks who present with cardiac symptoms would be helpful so far as determining the likelihood of complications in the patient's near future. See refer:

Journal of Thrombosis and Thrombolysis

Issue: Volume 18, Number 2

Date: October 2004

Pages: 109 - 115

#4 An instrument that tests for aspirin resistance (apparently a significant segment of the population is resistant)

Ideally then, testing for the efficacy of plavix therapy plus another assay for platelet alpha granule inhibition would be fairly ideal...especially if these assays can be performed with specificity/accuracy in a rapid, cheap manner.

I've reviewed several assays and methodologies comparing one to the other, and while CP (flow cytometry) which employs shear-dependent platelet function testing is superior to all both in terms of following patients short-term and long-term, it's expensive, time-consuming and isn't available 24/7 at most facilities. Aggregometry is also more cumbersome, but the RFPA (accumetrics) is almost as good as what the CP gives when a baseline value is run and submitted as a ratio with the data from the drug-induced inhibition. Fortunately, RFPA can check for the baseline concurrently with the degree of inhibition even though the patient has been on an inhibitor for weeks. See ref:

http://circ.ahajournals.org/cgi/content/full/103/11/1488

You mentioned the x and y values of graphing...the RFPA utilizes a different unit of measure (PAU) platelet aggregation units, which can then be translated into percentage of platelet activity (or inhibition). There are set percentages from which the user can determine to what degree the patient requires more or less anti-coagulation and then administer accordingly (i.e. the cath lab).

As far as how this platelet function testing translates into determining when a patient might need platelet transfusion and/or if there would be benefit despite other parameters...am still researching this, but believe this is basically covered under the plavix and aspirin patient population.

...still researching this topic...:spotlight :

We are going to be opening an Open Heart Center in June. Have been notified that a type of platelet function assay may be required. I've done some research and came across the Accumetrics system. Discussed this briefly with the cardiologist who will be in charge; he didn't seem to have an opinion or really know about the instrument or the claims made by the manufacturer.

Can anyone help me out? Is this system being utilized in other open heart centers? Are the docs using it to determine clinical significance when ordering platelets? Labgirl153: your situation sounds very close to mine, and I have similar thoughts. Have you resolved your issue there?

No resolution here yet...the pathologists are mum about it at this point and my dept. is out of the loop. Think a decision will occur during the summer but I have no more info on it. Sorry couldn't be of more help. It's likely you've read most of the papers I've read as well on this subject and particularly regarding the accumetrics system. I believe some cardiac institution in Texas has used and studied the accumetrics instrument, but can't get my hand on their papers right now. There's a Polish paper that was pretty well done too:

http://www.kardiologiapolska.pl/archieve.php?vol=60&iss=5&pg=459〈=en

When I find the papers from the Texas crew, will post those. Good luck.

Here too, is an abstract comparing the Accumetrics platelet assays to another product by Helena (the ICHOR). From what I understand, Helena is on more solid ground financially, since Accumetrics has been around <10 yrs. Radiometer once acquired Accumetrics but sold it. :coffeecup

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15815877&itool=iconabstr&query_hl=2&itool=pubmed_docsum