Free Platelet-Function Tests Boost Utilization, Don't Alter Treatment or Outcomes

November 04, 2013

SAN FRANCISCO, CA — Physicians are far more likely to order a VerifyNow (Accumetrics) platelet-function test for their patients with acute MI if the point-of-care assay is offered to them for free, but it only modestly influences their choice of antiplatelet agent and doesn't have any effect on 30-day risk of events, including bleeding.

Those observations were from a novel study presented here at TCT 2013 that gauged physicians' inclination to use the test, not just whether the test performed as advertised and made a clinical impact.

When physicians did order the test, which measures the aggressiveness of platelets and can help guide the choice of an ADP-receptor inhibitor, it was usually to switch the patient from clopidogrel to a more potent drug like prasugrel (Effient, Lilly/Daiichi-Sanyo) or, sometimes, ticagrelor (Brilinta, AstraZeneca). Much less often it was to raise the drug's dosage to achieve a stronger antiplatelet effect.

The study's lead investigator, Dr Tracy Wang (Duke Clinical Research Institute, Durham, NC), told heartwire that most likely ordering the test didn't change antiplatelet therapy much because "up front, there was already a higher use of the more potent antiplatelet agents, prasugrel or ticagrelor, than clopidogrel."

US physicians appear to be "intellectually interested in these platelet-function-test results," she said. But "we generally select an agent based on what we think a patient needs and what we think a patient can afford or can take. So in that setting, if the clinician's mind is already made up, introducing a test isn't likely to change that decision very much, although it does move the needle some, a small amount," she said.

After Wang's formal presentation of the study, called TRANSLATE-POPS , panelist Dr Robert A Byrne (Deutsches Herzzentrum, Munich, Germany) pressed further for reasons behind the physicians' "lack of enthusiasm" for platelet-function testing in the study.

One reason may have been a shortage of clear clinical-trial results to guide them. "We really are in a data-free zone with regard to the role of platelet-function testing in the ACS population," she said. "This may have tempered our clinicians' response to the test results."

Dr Cindy L Grines (Detroit Medical Center Cardiovascular Institute, MI) agreed for heartwire that recent trials have painted a confusing picture for clinicians about how to use the assay in patients with ST-elevation and non-ST-elevation MI (NSTEMI and STEMI) and whether it makes a clinical difference. "We do know that if you have high platelet reactivity, you do worse." Less clear is whether drug and dosage selection based on the assay affects outcomes.

The trial evenly randomized 100 hospitals across the US, centers that did not already routinely perform platelet-function testing for ACS patients (routinely defined as at least 30% of the time) to have the VerifyNow test provided free of charge (with encouragement to use it at least 12 hours after PCI for STEMI or NSTEMI) or to perform their usual care. After that, all treatment decisions were left up to physicians at the centers.

Usual care, which involved 1853 patients at 50 centers, could include platelet-function testing if physicians independently chose to use it, but the study did not provide it to them free or otherwise. There were 2013 patients participating at the 50 free-testing centers. In both groups, three-quarters were initially treated with clopidogrel and one quarter with prasugrel.

Testing was ordered for only 26 patients (1.4%) in the usual-care group but for 1336 patients (66.4%) in the free-access group.

Therapeutic adjustments were made 15.9% of the time in the free-access group vs 11.6% in the usual-care group, for an odds ratio (OR) of 1.55 (95% CI 1.11–2.17; p=0.01). The adjustments consisted of a dosage change in 1.6% and 1.1% of cases, respectively, and a switch to a different ADP-receptor inhibitor in 14.5% and 10.6% of cases, respectively (p=0.02). Usually the switch was from clopidogrel to one of the other agents.

The test's free availability had no significant impact on clinical outcomes.

Odds Ratio (95% CI) for Clinical Events, Free-Access to Testing Group vs Usual Care Group in TRANSLATE-POPS

30-day clinical outcomes OR (95% CI) p
MACE* 0.93 (0.66–1.31) 0.69
Bleeding by GUSTO criteria 0.80 (0.50–1.26) 0.33

*All-cause death, recurrent MI, stroke, unplanned coronary revascularization

Grines observed that an interventional cardiologist might be more inclined to order platelet-function tests for patients in whom adequate antiplatelet potency is especially important, including those considered at increased risk for stent thrombosis. And those tend to be the sickest patients, she said, such as those with large MIs, who receive multiple stents, have preexisting thrombus, diabetes, renal failure, congestive heart failure, or cardiogenic shock.

"So I would think about using it in those situations. But in the average patient? I'm not so sure they need it." Even in high-risk patients, she added, some physicians would just go ahead and use prasugrel or ticagrelor without testing.

At a press conference on TRANSLATE-POPS, Dr William W O'Neill (Henry Ford Hospital, Detroit, MI) pointed out that even higher-risk patients are a gray area for testing, and he's "always been worried" about whether patients with complex target lesions are adequately protected by clopidogrel. He suggested to Wang that "when you publish," he would like to see the numbers by how many stents used, for what kind of lesion, and in what coronary artery.

Wang said the study population included "a couple percentage" of patients who received stents in their left main coronary arteries and about 12% had multivessel stenting. When they broke out the data by lesion location and complexity, "we did not see any difference in therapeutic adjustments."

The study was sponsored by Daiichi Sankyo and Eli Lilly. Wang disclosed receiving research grants at her center from Daiichi Sankyo, Eli Lilly, Gilead Sciences, and GlaxoSmithKline and honoraria from AstraZeneca.


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