AHA: Some platelet reactivity tests get thumbs up from new trial
Orlando, Fla.—Three out of six platelet function tests can identify heart patients whose platelet reactivity will increase heart risk, despite being pretreated with two anti-clotting drugs before PCI, according to a Sunday presentation during the late-breaking clinical session at the American Heart Association conference. The co-principal investigators told Cardiovascular Business News that their findings support more widespread use of platelet reactivity testing with these three tests.

Up to 36 percent of patients are less responsive to clopidogrel, according to co-principal investigator Jurrien M. ten Berg, MD, PhD, an interventional cardiologist at St. Antonius Hospital in Nieuwegein, the Netherlands. He said that the clinical literature indicates that high on-treatment platelet reactivity is associated with thrombotic events, adding that the best platelet function test to predict clinical outcome is “unknown.”

The POPular (Do Platelet function assays predict clinical Outcomes in clopidogrel pretreated patients undergoing elective PCI) is the first head-to-head comparison of multiple function tests in predicting thrombotic and bleeding events.

The researchers compared six different tests of platelet reactivity in 1,069 consecutive patients under PCI, and included a one-year follow up. The tests are light transmittance aggregometry (LTA), Accumetrics’ VerifyNow P2Y12 assay, Helena Laboratories’ Plateletworks, Matis Medical’s Impact-R, PFA-100 system and Siemens Healthcare Diagnostics’ Innovance PFA P2Y (which is not available for sale, as its under development).

The primary endpoint was a composite of all-cause death, MI, urgent revascularization, stroke or stent thrombosis.

Berg reported that patients who had high platelet reactivity on three of the tests—LTA, VerifyNow P2Y12 and Plateletworks—had a significantly greater incidence of the combined primary endpoint (12.1 vs. 6 percent) at one year compared to patients who did not. The three other tests evaluated didn’t predict, ten Berg reported.

Co-principal investigator Nicoline J. Breet, PhD, a fellow and cardiologist-in-training at St. Antonius, said in an interview that it is unclear why the other tests did not perform well. “These sheer-stressed based tests assess the physiological measurement of platelet function,” she explained.

Also, in his commentary of the trial, Dietmar Trenk, PhD, of the Herz-Zentrum Bad Krozingen in Bad Krozingen, Germany, mentioned that “shear-stress induced adhesion based methods are not useful.” Trenk also said that there are other available tests predicting adverse clinical outcomes, including the multiple electrode platelet aggregometry and the VASP test.

In an interview, ten Berg said that the tests vary greatly, even in terms of time consumption. Of the three predictive tests, the LTA is the most-labor intensive and can’t be performed at bedside, but  requires blood manipulation by trained personnel in a laboratory, which takes several hours. However, he added that Plateletworks must be done within 10 minutes of drawing blood, and “VerifyNow P2Y12 does not have those limitations and only takes a couple of minutes.”

In advocating for wider use of the tests, ten Berg says that physicians base their clinical decisions on a variety of patient characteristics, such as age, diabetes or left ventricular function, and these platelet function measurements will only add to the accuracy of their decisions.

“Only a minority of centers routinely uses platelet reactivity testing to guide therapy, but it is used extensively as a research tool,” ten Berg said. “I think we are on the brink of making platelet reactivity a clinical tool.

He noted that logistics and finance have served as hindrances to adoption, because the tests are not reimbursed in either Germany or the United States.

Despite these concerns, ten Berg, Breet and colleagues concluded that it is “useful to test the response to antiplatelet therapy in all patients at highest risk for clot-related complications.”

The researchers acknowledged that their results have not yet been extended to demonstrate that basing additional treatment(s) on test results would improve patient outcomes in those at higher risk.

The study received no funding; however, Siemens Healthcare Diagnostics provided the Dade PFA Collagen/ADP Test Cartridge, as well as the work-in-progress Innovance PFA P2Y free-of-charge.