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Platelet function tests don’t predict PCI outcomes in low-risk patients

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – Baseline platelet function is only modestly related to ischemic outcomes after percutaneous coronary intervention (PCI) in low-risk patients, according to a study in more than 1000 patients. Moreover, common assays don’t accurately predict bleeding risk.

High platelet reactivity is known to increase patients’ risk for atherothrombotic events after PCI, and several assays are available for quantifying reactivity, the research team notes in the February 24th Journal of the American Medical Association.

In an attempt to identify the most accurate test, Dr. Jurrien M. ten Berg and colleagues at St. Antonius Hospital, Nieuwegein, the Netherlands, analyzed blood samples from 1069 low-risk patients on optimal clopidogrel and aspirin treatment, in advance of PCI and stent implantation.

They compared six different tests in subsets of patients:

— Light transmittance aggregometry (n = 1051)
— VerifyNow P2Y12 (Accumetrics) (n = 1052)
— Plateletworks (Helena Laboratories) (n = 606)
— IMPACT-R (Matis Medical Inc.) (n = 910)
— Dade PFA-100 (Siemens Healthcare Diagnostics Products CmbH) (n = 812)
— Innovance PFA P2Y (Siemens Healthcare Diagnostics Products CmbH) (n = 588)

The primary end point was a composite of all-cause death, acute myocardial infarction, ischemic stroke, and stent thrombosis. The primary safety outcome was major and minor bleeding. High platelet reactivity was based on a cut-off defined with receiver operating characteristic curve analysis.

During 1 year of follow-up, 18 patients died, 64 had nonfatal acute myocardial infarction, 14 had nonfatal ischemic strokes, 13 had definite stent thrombosis, and 3 had possible stent thrombosis. Thirty-three had major bleeding; 24 had minor bleeding.

When the authors constructed a model that would identify predictors for the primary endpoint, high platelet reactivity significantly improved the area under the curve only when measured by three of the methods: light transmittance aggregometry, the VerifyNow PsY12 assay, and the Plateletworks assay.

Specifically, rates of the primary end point in patients with and without high platelet reactivity were 11.7% vs 6.0% with light transmittance aggregometry (p < 0.001), 13.3% vs 5.7% with the VerifyNow PsY12 assay (p < 0.001), and 12.6% vs 6.1% with the Plateletworks assay (p = 0.005). Still, Dr. ten Berg’s team notes, “the predictive accuracy of these tests was only modest.” None of the tests could discriminate between patients with and without bleeding. The investigators note that the sample size of the Innovance PFA P2Y, which became available halfway through the trial, was underpowered to detect a link between platelet reactivity and outcome, and other tests not available at the time were excluded. Also, patients were on 3 different clopidogrel regiments. “However, these 3 regimens are current clinical practices and our study therefore reflects the clinical relevance of monitoring platelet function in daily practice,” the authors add. Until several ongoing clinical trials are completed, the authors maintain, “clinical practice should not be guided by (point-of-care) platelet function testing” for low-risk patients undergoing elective PCI. Siemens Healthcare Diagnostics provided the Dade PFA and Innovance PFA P2Y for the study without charge. Reference:
JAMA 2010;303:754-762.