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Laboratory measurement of platelet reactivity: consider the impact of new drugs, generic options and healthcare economics.

More than 50 million Americans take a daily aspirin in an effort to reduce the risk of heart attacks. Plavix[R] (clopidogrel) is the second-biggest selling prescription drug worldwide, with almost 30 million prescriptions filled annually. (1) This drug is taken to reduce platelet reactivity, which can lead to heart attack, stroke, and death. Yet it has been well established that there is a high degree of individual variability in response to clopidogrel and similar drugs, with approximately one in three patients not responding adequately. (2) Patients who do not respond adequately may be at significantly greater risk for major adverse cardiac events. (3-7) The introduction of newer antiplatelet drugs as well as generic versions of clopidogrel, following Plavix's loss of patent protection on May 17, 2012, changes the economic incentives that are associated with managing these risks. In this scenario, laboratory medicine can play a critical role in clinical decision making.

Transformation of healthcare

Healthcare is transforming, especially as the new science of personalized medicine takes some of the emphasis from more traditional diagnostics to more accurate tailored disease diagnostics and management. Today. rapid testing provides fast, actionable information that reduces the time to diagnosis, treatment, and cure.

For individuals taking antiplatelet medications, platelet reactivity testing measures levels of platelet reactivity. There is a high degree of bio-variability in response due to multiple genetic factors (e.g., CYP2C 19 polymorphisms), cellular factors (e.g.. variant expression of enzymes), and clinical factors (e.g., diabetes). Platelet reactivity testing provides clinicians with real-time laboratory data, and can be provided on demand, during any shift, any day, as well as around the clock if needed, thereby allowing rapid interventions by clinicians. Such interventions can reduce morbidity and mortality and improve patient safety, in addition to improving quality and cost outcomes.

Improving both cost and quality

With the advent of lower-cost generic clopidogrel. there may be copay reductions for patients and drug cost reductions for healthcare systems. However, with the variability in response to clopidogrel, saving money on a generic drug may not reduce total healthcare costs if it leads to more patients returning to the hospital due to heart attacks, stroke, etc. Patients who do not respond adequately to their antiplatelet medications have a higher 30-day readmission rate than patients who are responding adequately. (8)

Platelet reactivity testing in the lab

To assess the effect of antiplatelet therapy, the standard has become light transmission and whole blood aggregation, which have been incorporated into a newer generation of point-of-care platelet function analyzers. In these instruments, ADP is contained in the reagents in order to initiate activity of the platelet P2Y12 receptor. Substances known to specifically block the platelet's P2Y 12 receptor include the thienopyridine class of drugs, including clopidogrel, prasugrel, ticagrelor, and ticlopidine. Aggregation results report the amount of ADP receptor-mediated aggregation specific to these platelet receptors, and the degree of platelet receptor blockade is reported by a change in light transmittance as the platelets bind fibrinogen and aggregate.

Platelet function is controlled by both genes and environment. The incorporation of both platelet function and genetic testing is necessary to personalize P2Y12 antiplatelet therapy. The effective evaluation of platelet function for patients receiving antiplatelet therapy requires a rapid TAT, low complexity. 24/7 availability, and results associated with defined patient outcomes. New point-of-care whole blood platelet function analyzers meet these requirements and provide results that most closely resemble platelet aggregation.

Platelet reactivity testing in clinical practice

Richard Shlofmitz, MD. Chairman, Department of Cardiology at St. Francis Hospital in Roslyn, New York, uses platelet reactivity testing in his interventional cardiology practice for patients who have had a PCI (percutaneous coronary intervention--i.e., a stent procedure). "I can rapidly receive a PRU result from the platelet reactivity test we utilize and make informed therapy decisions based on what I know to be important factors affecting my individual patients. For a patient with a drug-eluting stent, it is critical to have sufficient platelet inhibition. If you don't assess patients' platelet reactivity. you cannot be sure that you have platelet inhibition."

Quality improvement and value assessment

Many facilities are integrating laboratory medicine into quality improvement initiatives. These initiatives often yield positive economic outcomes in addition to improved quality metrics. Models are created to support these types of initiatives. One such model, a Quality Improvement and Value Assessment Tool, incorporates platelet reactivity testing to estimate and model the potential impact of integrating platelet reactivity testing into cardiovascular patient care.(9) This model examines two scenarios: I) the potential reduction in 30-day hospital readmissions following stent procedures, resulting from the measurement of platelet reactivity and modification of antiplatelet therapy to achieve a target level; and 2) the potential reduction in pre-op medical admission days for CABG patients. resulting from measurement of platelet reactivity and determination of when CABG patients would no longer be displaying an antiplatelet effect following discontinuation of a P2Y 12 inhibitor.

Laboratories can play a critical role in the transformation of healthcare to a more personalized approach. yielding better quality and cost outcomes for the entire healthcare system. The offering of platelet reactivity testing is a compelling example of laboratory leadership driving improvements that benefit patients. physicians, and healthcare administration.

References

(1.) IMS Institute for Healthcare Informatics, April 2011.

(2.) Dupont AG, Gabriel DA, Cohen MG. Antiplatelet therapies and the role of antiplatelet resistance in acute coronary syndrome. Thromb Res. 2009;124(1):6-13.

(3.) Patti G, et al. Point-of-care measurement of clopidogrel responsiveness predicts clinical outcome in patients undergoing percutaneous coronary intervention. J Am Coll Cardiol. 2008;52:1128-1133.

(4.) Marcucci R, et al Cardiovascular death and nonfatal myocardial infarction in acute coronary syndrome patients receiving coronary stenting are predicted by residual platelet reactivity to ADP detected by a point-of-care assay. Circulation. 2009;119(2):237-242.

(5.) Cuissett T, et al. Relation of low response to clopidogrel assessed with point-of-care assay to periprocedural myonecrosis in patients undergoing elective coronary stenting for stable angina pectoris. Am J Cardiol 2008;101(12):1700-1703.

(6.) Price MJ, et al. Prognostic significance of post-clopidogrel platelet reactivity assessed by a point-of-care assay on thrombotic events after drug-eluting stem implantation. Eur Heart J. 2008;29(8):992-1000.

(7.) Brar SS, et al. Impact of platelet reactivity on clinical outcomes after percutaneous coronary intervention. J Am Coll Cardiol. 2011;58(19):1945-1954.

(8.) Wiviott SD, Braunwald E, McCabe CH, et al for the Triton-TIMI 38 investigators. Prasugrel versus clopidogrel in patients with acute coronary syndromes. N Engl J Med. 2007;357:2001-15.

(9.) Mackowiak J, et al. An economic model incorporating a point of care platelet function assay: a quality improvement and value assessment tool. Abstract accepted for AACC National Meeting, July 2012.

By Denise Uettwiller-Geiger, PhD, DLM(ASCP), and John Mackowiak, PhD

Denise Uettwiller-Geiger, PhD, DLM (ASCP), is Director of Laboratory Services & Clinical Trials at John T. Mather Memorial Hospital in Port Jefferson, NW. John Mackowiak, PhD, is President of the Center for Outcomes Research, Nashville, TN.
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Title Annotation:Tips from the clinical experts
Author:Uettwiller-Geiger, Denise; Mackowiak, John
Publication:Medical Laboratory Observer
Date:Jul 1, 2012
Words:1156
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