Evaluation of an automated von Willebrand factor glycoprotein IbM activity assay compared with 3 alternative von Willebrand factor activity assays.

Background: To overcome deficiencies of the traditional von Willebrand factor (VWF) ristocetin cofactor activity assay (VWF:RCo), several automated assays for VWF platelet-binding activity have been developed. Information on the performance of these assays and their diagnostic utility remains limited. Objectives: To validate the VWF:glycoprotein IbM assay INNOVANCE VWF Ac and compare it with an automated VWF:RCo assay as well as with an automated assay and a manual VWF:Ab assay and to generate reference ranges and analyze reproducibility of the VWF:glycoprotein IbM assay. Methods: Clinical sites enrolled healthy subjects and patients representing the intended use population; VWF activity assays were performed, and results were analyzed. The performance of the INNOVANCE VWF Ac assay was also compared between the BCS XP System and the CS-2500 and CS-5100 analyzers. Results: The INNOVANCE VWF Ac assay correlated well with the VWF:RCo assay and the automated HemosIL VWF:Ab assay, with Pearson coefficients of >.9 and a predicted bias of ≤5.0 IU/dL at VWF levels of 30 IU/dL and ≤5.8 IU/dL at the levels of 50 IU/dL, but correlation and bias were not as good when compared with the REAADS manual VWF:Ab assay. Reference ranges observed for healthy subjects correlated well with previously published findings. Reproducibility of the INNOVANCE VWF Ac assay on the BCS XP System and the CS analyzers was excellent, as was correlation among devices. Conclusion: The characteristics of the INNOVANCE VWF Ac assay regarding comparability with other VWF activity assays, reference ranges, and precision support the use of this assay for evaluation of patients with concern for von Willebrand disease.

The relation between ABO blood types and clinical and platelet function parameters in patients who underwent percutaneous coronary intervention.

BACKGROUND: ABO blood groups have been associated with venous thromboembolism and arterial thrombosis. Although platelets play key roles in thrombogenesis, the relation between ABO groups and platelets is not well known and was investigated in this study. PATIENTS AND METHODS: ABO blood type information was retrospectively obtained for 206 patients who underwent percutaneous coronary intervention (PCI) and received dual antiplatelet therapy with aspirin and clopidogrel. Platelet function was measured using VerifyNow system, light transmission aggregometry, thromboxane B2, urinary 11-dehydrothromboxane B2, and vasodilator-stimulated phosphoprotein phosphorylation assays. Samples were also tested following treatment with 10 and 30 µmol/l of aspirin or 30 and 100 µmol/l of P2Y12 inhibitor 2-methylthioadenosine 5'-monophosphate triethylammonium salt hydrate (2-MeSAMP). Forty-four clinical and 30 platelet function parameters were analyzed. Patients were categorized as aspirin or clopidogrel poor responder (PR) according to cutoff levels of each test. RESULTS: Blood type A was significantly associated with myocardial infarction (MI) history [odds ratio (OR)=2.50, 95% confidence interval (CI)=1.37-4.58, P=0.003], higher baseline troponin T and creatine kinase-MB (CK-MB) index, post-PCI CK-MB index, and platelet reactivity index (PRI), and being PR against 2-MeSAMP (OR=5.75, 95% CI=1.51-21.90, P=0.010). Blood type O was associated with higher arachidonic acid-induced platelet aggregation and negatively associated with MI history (OR=0.47, 95% CI=0.26-0.84, P=0.010), PRI and being PR against clopidogrel (OR=0.54, 95% CI=0.30-0.99, P=0.043) and 2-MeSAMP (OR=0.16, 95% CI=0.03-0.76, P=0.021). CONCLUSION: Blood type A was found as a risk factor for MI. Higher arachidonic acid-induced aggregation in group O and higher PRI in group A against aspirin and P2Y12 inhibitor treatment, respectively, may suggest alternative antiplatelet therapies for PRs with these blood types.

Establishing a Clinical Laboratory in a Tertiary/Quaternary Care Greenfield Hospital in the Middle East: Recounting the Cleveland Clinic Abu Dhabi Experience.

CONTEXT: - This review chronicles the establishment of a clinical laboratory in Cleveland Clinic Abu Dhabi, a greenfield tertiary/quaternary care hospital in the United Arab Emirates. It discusses the challenges faced, solutions sought, and lessons learned and shares insights and pitfalls that may be encountered in such an undertaking. OBJECTIVES: - To share our experience in building a clinical laboratory in a start-up, multispecialty hospital and how we provided support and managed people, processes, and technology for building and making operational the Cleveland Clinic Abu Dhabi. DATA SOURCES: - The Medline (PubMed, National Center for Biotechnology Information, Bethesda, Maryland) database was used to review this topic as well as other journals, books, and Google (Mountain View, California) search engine. CONCLUSIONS: - To deliver on the promise of quality healthcare in a culturally appropriate setting close to home, Cleveland Clinic Abu Dhabi proved to be an unprecedented and ambitious project, jointly carried out by Mubadala Investment Corporation and the Cleveland Clinic Foundation. Cognizant of the scale of this task, hospital leadership engaged closely with staff and stakeholders through motivational techniques and effective communication. Excellent project planning and execution of complex tasks were required for initiation of services. Establishing the clinical laboratory served as an instructive model in fostering multidisciplinary teamwork by highlighting ways to manage operational roadblocks and opportunities in the planning, commissioning, and activation phases. Throughout the activation process, all efforts were directed to create a patient-safety culture within an intentional-learning organization.

The Impact of an Electronic Expensive Test Notification.

OBJECTIVES: The impact of clinical decision support tools (CDSTs) that display test cost information has been variable. METHODS: We retrospectively analyzed the 3-year impact of a passive CDST that notified providers when the test order cost was $1,000 or more. We determined the most common expensive tests ordered, the frequency with which providers abandoned the order after notification, and the costs saved through this intervention. RESULTS: The average monthly abandonment rate was 12.5% (2014), 12.9% (2015), and 14.3% (2016). The cost savings from tests not performed for this 3-year period was $696,007. Molecular hematopathology assays were the most frequently ordered tests, with variable abandonment rates. CONCLUSIONS: Although this CDST was passive (ie, could be overridden at the point of order entry) and was associated with a relatively low abandonment rate, it achieved a considerable cost savings each year since each abandoned test saved the institution $1,000 or more.

In vivo evaluation of biomimetic fluorosurfactant polymer-coated expanded polytetrafluoroethylene vascular grafts in a porcine carotid artery bypass model.

OBJECTIVE: The objective of this study was to evaluate the potential for biomimetic self-assembling fluorosurfactant polymer (FSP) coatings incorporating heptamaltose (M7-FSP) to block nonspecific protein adsorption, the cell adhesive RGD peptide (RGD-FSP), or the endothelial cell-selective CRRETAWAC peptide (cRRE-FSP) to improve patency and endothelialization in small-diameter expanded polytetrafluoroethylene (ePTFE) vascular graft implants. METHODS: ePTFE vascular grafts (4 mm in diameter, 5 cm in length) were coated with M7-FSP, RGD-FSP, or cRRE-FSP by dissolving FSPs in distilled water and flowing solution through the graft lumen for 24 hours. Coatings were confirmed by receding water contact angle measurements on the lumen surface. RGD-FSP and cRRE-FSP grafts were presodded in vitro with porcine pulmonary artery endothelial cells (PPAECs) using a custom-designed flow system. PPAEC coverage on the lumen surface was visualized with epifluorescent microscopy and quantified. Grafts were implanted as carotid artery interposition bypass grafts in seven pigs for 33 ± 2 days (ePTFE, n = 3; M7-FSP, n = 4; RGD-FSP, n = 3; cRRE-FSP, n = 4). Patency was confirmed immediately after implantation with duplex color flow ultrasound and at explantation with contrast-enhanced angiography. Grafts were sectioned for histology and stained: Movat pentachrome stain to outline vascular layers, immunofluorescent staining to identify endothelial cells (anti-von Willebrand factor antibody), and immunohistochemical staining to identify smooth muscle cells (anti-smooth muscle α-actin antibody). Neointima to lumen area ratio was determined to evaluate neointimal hyperplasia. RESULTS: Receding water contact angle measurements on graft luminal surfaces were significantly lower (P < .05) on FSP-coated ePTFE surfaces (M7-FSP, 40 ± 16 degrees; RGD-FSP, 25 ± 10 degrees; cRRE-FSP, 33 ± 16 degrees) compared with uncoated ePTFE (126 ± 2 degrees), confirming presence of the FSP layer. In vitro sodding of PPAECs on RGD-FSP and cRRE-FSP grafts resulted in a confluent monolayer of PPAECs on the luminal surface, with a similar cell population on RGD-FSP (1200 ± 187 cells/mm(2)) and cRRE-FSP (1134 ± 153 cells/mm(2)) grafts. All grafts were patent immediately after implantation, and one of three uncoated, two of three RGD-FSP, two of four M7-FSP, and two of four cRRE-FSP grafts remained patent after 1 month. PPAEC coverage of the lumen surface was seen in all patent grafts. RGD-FSP grafts had a slightly higher neointima to lumen area ratio (0.53 ± 0.06) compared with uncoated (0.29 ± 0.15), M7-FSP (0.20 ± 0.15), or cRRE-FSP (0.17 ± 0.09) grafts. CONCLUSIONS: Biomimetic FSP-coated ePTFE grafts can be used successfully in vivo and have potential to support endothelialization. Grafts modified with the M7-FSP and cRRE-FSP showed lower intimal hyperplasia compared with RGD-FSP grafts.

Dual biofunctional polymer modifications to address endothelialization and smooth muscle cell integration of ePTFE vascular grafts.

Expanded polytetrafluoroethylene (ePTFE) grafts were coated on the luminal surface with a cell-adhesive fluorosurfactant (FSP) polymer to promote endothelialization, followed by ethanol hydration to degas the pores and subsequent cell-adhesive, enzymatically degradable poly(ethylene glycol)-based hydrogel incorporation into the graft interstices to accommodate potential smooth muscle cell integration in the graft wall. The FSP coating on ePTFE was stable as demonstrated by a significantly reduced receding water contact angle on FSP-coated ePTFE (14.5 ± 6.4°) compared to uncoated ePTFE (105.3 ± 4.5°, P < 0.05) after ethanol exposure. X-ray photoelectron spectroscopy analysis of the same surfaces confirmed FSP presence. Localization of the FSP and hydrogel within the ePTFE graft construct was assessed using fluorescently labeled polymers, and demonstrated hydrogel infiltration throughout the thickness of the graft wall, with FSP coating limited to the lumen and adventitial surfaces. FSP at the luminal surface on dual-coated grafts was able to bind endothelial cells (EC) (98.7 ± 23.1 cells/mm(2) ) similar to fibronectin controls (129.4 ± 40.7 cells/mm(2) ), and significantly higher than uncoated ePTFE (31.6 ± 19 cells/mm(2,) P < 0.05). These results indicate that ePTFE grafts can be simultaneously modified with two different polymers that have potential to directly address both endothelialization and intimal hyperplasia. Such a construct is a promising candidate for an off-the-shelf synthetic graft for small-diameter graft applications.

Reducing duplicate testing: a comparison of two clinical decision support tools.

OBJECTIVES: Unnecessary duplicate laboratory testing is common and costly. Systems-based means to avert unnecessary testing should be investigated and employed. METHODS: We compared the effectiveness and cost savings associated with two clinical decision support tools to stop duplicate testing. The Hard Stop required telephone contact with the laboratory and justification to have the duplicate test performed, whereas the Smart Alert allowed the provider to bypass the alert at the point of order entry without justification. RESULTS: The Hard Stop alert was significantly more effective than the Smart Alert (92.3% vs 42.6%, respectively; P < .0001). The cost savings realized per alert activation was $16.08/alert for the Hard Stop alert vs $3.52/alert for the Smart Alert. CONCLUSIONS: Structural and process changes that require laboratory contact and justification for duplicate testing are more effective than interventions that allow providers to bypass alerts without justification at point of computerized physician order entry.

Improving Molecular Genetic Test Utilization through Order Restriction, Test Review, and Guidance.

The ordering of molecular genetic tests by health providers not well trained in genetics may have a variety of untoward effects. These include the selection of inappropriate tests, the ordering of panels when the assessment of individual or fewer genes would be more appropriate, inaccurate result interpretation and inappropriate patient guidance, and significant unwarranted cost expenditure. We sought to improve the utilization of molecular genetic tests by requiring providers without specialty training in genetics to use genetic counselors and molecular genetic pathologists to assist in test selection. We used a genetic and genomic test review process wherein the laboratory-based genetic counselor performed the preanalytic assessment of test orders and test triage. Test indication and clinical findings were evaluated against the test panel composition, methods, and test limitations under the supervision of the molecular genetic pathologist. These test utilization management efforts resulted in a decrease in genetic test ordering and a gross cost savings of $1,531,913 since the inception of these programs in September 2011 through December 2013. The combination of limiting the availability of complex genetic tests and providing guidance regarding appropriate test strategies is an effective way to improve genetic tests, contributing to judicious use of limited health care resources.

Photoinitiator-free synthesis of endothelial cell-adhesive and enzymatically degradable hydrogels.

We report on a photoinitiator-free synthetic method of incorporating bioactivity into poly(ethylene glycol) (PEG) hydrogels in order to control physical properties, enzymatic biodegradability and cell-specific adhesiveness of the polymer network, while eliminating the need for UV-mediated photopolymerization. To accomplish this, hydrogel networks were polymerized using Michael addition with four-arm PEG acrylate (10 kDa), using a collagenase-sensitive peptide (CSP) as a crosslinker, and introducing an endothelial cell-adhesive peptide either terminally (RGD) or attached to the crosslinking peptide sequence (CSP-RGD). The efficiency of the Michael addition reactions were determined by nuclear magnetic resonance and Ellman's assay. Successful decoupling of cell adhesivity and physical properties was demonstrated by quantifying and comparing the swelling ratios and Young's moduli of various hydrogel formulations. Degradation profiles were established by incubating functionalized hydrogels in collagenase solutions (0.0-1.0 µg ml(-1)), demonstrating that functionalized hydrogels degraded at a rate dependent upon collagenase concentration. Moreover, it was shown that the degradation rate was independent of CSP-RGD concentration. Cell attachment and proliferation on functionalized hydrogels were compared for various RGD concentrations, providing evidence that cell attachment and proliferation were directly related to relative amounts of the CSP-RGD combination peptide. An increase in cell viability was achieved using Michael addition techniques when compared to UV polymerization, and was assessed by a LIVE/DEAD fluorescence assay. This photoinitiator-free method shows promise in creating hydrogel-based tissue engineering scaffolds allow for decoupled cell adhesivity and physical properties and that render greater cell viability.

Extracellular matrix-mimetic poly(ethylene glycol) hydrogels engineered to regulate smooth muscle cell proliferation in 3-D.

The goal of this project is to engineer a defined, synthetic poly(ethylene glycol) (PEG) hydrogel as a model system to investigate smooth muscle cell (SMC) proliferation in three-dimensions (3-D). To mimic the properties of extracellular matrix, both cell-adhesive peptide (GRGDSP) and matrix metalloproteinase (MMP) sensitive peptide (VPMSMRGG or GPQGIAGQ) were incorporated into the PEG macromer chain. Copolymerization of the biomimetic macromers results in the formation of bioactive hydrogels with the dual properties of cell adhesion and proteolytic degradation. Using these biomimetic scaffolds, the authors studied the effect of scaffold properties, including RGD concentration, MMP sensitivity, and network crosslinking density, as well as heparin as an exogenous factor on 3-D SMC proliferation. The results indicated that the incorporation of cell-adhesive ligand significantly enhanced SMC spreading and proliferation, with cell-adhesive ligand concentration mediating 3-D SMC proliferation in a biphasic manner. The faster degrading hydrogels promoted SMC proliferation and spreading. In addition, 3-D SMC proliferation was inhibited by increasing network crosslinking density and exogenous heparin treatment. These constructs are a good model system for studying the effect of hydrogel properties on SMC functions and show promise as a tissue engineering platform for vascular in vivo applications.

Multi-parameter assessment of platelet inhibition and its stability during aspirin and clopidogrel therapy.

INTRODUCTION: Poor response to antiplatelet drugs is associated with adverse outcomes. We assessed platelet inhibition and its stability and tested correlation and agreement between platelet function assays. METHODS: Peripheral blood from 58 patients on both aspirin and clopidogrel who underwent percutaneous coronary intervention (PCI) was collected at hospital discharge (visit-1) and at 30-90 days (visit-2). Platelet function was measured using light transmission aggregometry (LTA-AA and LTA-ADP), VerifyNow® (Aspirin; ARU and P2Y12; PRU), ex vivo TxB2, urinary 11dhTxB2, and VASP (PRI) assays. Data were analyzed as continuous, quartiles and binary. Patients were defined as aspirin poor responder (PR) with ARU ≥ 550, LTA-AA maximum ≥ 20%, TxB2 ≥ 1 ng/mL or 11dhTxB2 ≥ 1,500 pg/mg of creatinine and as clopidogrel PR with PRU ≥ 240, PRU ≥ 208, LTA-ADP maximum ≥ 40%, PRI ≥ 50%, or PRI ≥66%. RESULTS: Aspirin PR was 3-33% and clopidogrel PR was 10-35% in visit-1. LTA-AA, 11dhTxB2, and all clopidogrel-response measures showed correlation and agreement between visit-1 and visit-2. The highest agreement between two visits was revealed by PRU ≥ 240 and PRI ≥ 66% (PRU-κ=0.7, 95% CI=0.47, 0.93; PRI-κ=0.69, 95% CI=0.42, 0.95, p-values<0.001). Comparison of platelet function assays in a single visit (visit-1) revealed a poor correlation between LTA-AA and 11dhTxB2 assays and no agreement among aspirin-response assays. The highest correlation and agreement were obtained between VerifyNow® P2Y12 and VASP assays (rho=0.7, p-value<0.001 and PRU ≥ 208-PRI-κ=0.41-0.42, 95% CI=0.13, 0.69, p-values<0.001). CONCLUSIONS: Platelet inhibition is stable during aspirin and clopidogrel treatment. Clopidogrel-response assays correlate and agree with each other better than aspirin-response assays.

Duplicate laboratory test reduction using a clinical decision support tool.

OBJECTIVES: Duplicate laboratory tests that are unwarranted increase unnecessary phlebotomy, which contributes to iatrogenic anemia, decreased patient satisfaction, and increased health care costs. MATERIALS AND METHODS: We employed a clinical decision support tool (CDST) to block unnecessary duplicate test orders during the computerized physician order entry (CPOE) process. We assessed laboratory cost savings after 2 years and searched for untoward patient events associated with this intervention. RESULTS: This CDST blocked 11,790 unnecessary duplicate test orders in these 2 years, which resulted in a cost savings of $183,586. There were no untoward effects reported associated with this intervention. CONCLUSIONS: The movement to CPOE affords real-time interaction between the laboratory and the physician through CDSTs that signal duplicate orders. These interactions save health care dollars and should also increase patient satisfaction and well-being.

Algorithmic approaches to hemostasis testing.

There are many unique issues that may make a pathologist's consultation helpful in hemostasis testing. Besides the rapidly expanding knowledge of both bleeding and thrombotic disorders and a wide test menu, hemostasis testing is very sensitive to preanalytical issues (hemolysis, fill volume, time, temperature, storage conditions) and the interference of many commonly prescribed drugs. The pathologist can serve an important role in the evaluation of a patient for a bleeding or thrombotic disorder. Using defined algorithms, hemostasis testing can proceed in a logical fashion and be reported using patient-specific comments that take into account clinical history and medication therapy. This approach can improve the diagnostic process, preventing misdiagnoses and leading to a decreased time to diagnosis and an improved utilization of laboratory resources.

Biomimetic-engineered poly (ethylene glycol) hydrogel for smooth muscle cell migration.

We report on a biomimetic scaffold as a model system to evaluate smooth muscle cell (SMC) migration in three dimensions. To accomplish this, bio-inert poly (ethylene glycol) (PEG)-based hydrogels were designed as the scaffold substrate. To mimic properties of the extracellular matrix, cell-adhesive peptide (GRGDSP) derived from fibronectin and collagenase-sensitive peptide (GPQGIAGQ) derived from collagen type I were incorporated into the PEG macromer chain. Copolymerization of the biomimetic macromers results in the formation of bioactive PEG hydrogels with cell adhesivity and biodegradability. By utilizing these biomimetic scaffolds, we studied the effect of adhesive ligand concentration, proteolysis, and network cross-linking density on cell migration. Our results showed that three-dimensional SMC migration has a biphasic dependence on adhesive ligand density, and both adhesive and collagenase-sensitive peptides were required for cell migration to occur. Furthermore, network cross-linking density was shown to dramatically influence the behavior of cell migration in the hydrogels.

Cross-reactivity of cell-selective CRRETAWAC peptide with human and porcine endothelial cells.

We report on the cross-reactivity of the cell adhesive peptide CRRETAWAC between human and porcine endothelial cells (ECs). CRRETAWAC is a phage display derived peptide which has been shown to bind the α5 ß1 receptor on human ECs, but does not bind platelets and thus could be incorporated into a coating for cardiovascular biomaterials that resists platelet adhesion and thrombosis, while allowing for endothelialization. To determine the cross-reactivity of the peptide, attachment and growth of human and porcine ECs on CRRETAWAC fluorosurfactant polymer (FSP) coated surfaces was explored. CRRETAWAC FSP was synthesized and characterized by mass spectrometry, NMR, and IR spectroscopy. pEC attachment and growth on CRRETAWAC FSP was similar to the positive controls, human fibronectin and RGD FSP, achieving confluence in 72 h. Initial adhesion on CRRETAWAC FSP was also similar for porcine and human ECs. Blocking with soluble CRRETAWAC peptide reduced adhesion to CRRETAWAC coated surfaces by over 50%, indicating that the pECs specifically bind CRRETAWAC peptide. With this study, we have demonstrated that CRRETAWAC peptide coated surfaces are capable of binding porcine ECs in a specific manner and supporting a confluent layer of pECs. In vitro validation of the porcine model was critical for ensuring the best chance of success for the in vivo testing of CRRETAWAC coated ePTFE vascular grafts.

External quality assurance of fibrinogen assays using normal plasma: results of the 2008 College of American Pathologists proficiency testing program in coagulation.

CONTEXT: Proper diagnosis and therapy of fibrinogen deficiency requires high-quality fibrinogen assays. OBJECTIVE: To assess the interlaboratory bias, precision, and grading of fibrinogen assays used by laboratories participating in the United States College of American Pathologists proficiency testing program in coagulation. DESIGN: Two identical vials of normal plasma were sent to more than 3500 laboratories. Participants measured fibrinogen levels using local methods. RESULTS: Fifty different fibrinogen methods were evaluated. All-method bias was 8.3% (range of method-specific biases, 0.0%-27.0%) and all-method coefficient of variation was 7.7% (range of method-specific coefficients of variation, 0.7%-25.8%). After controlling for reagent/instrument type, mean fibrinogen levels were 11.6% higher for prothrombin time-based reagents compared to Clauss (P < .001), and coefficient of variation was 46% lower for mechanical endpoint instruments compared to photo-optical. Most testing events (97.4%) could be reliably graded as pass or fail using a target range of ±20% from the method mean (total pass rate, 98.8%). Total fail rate was 3.0-fold lower for mechanical instruments compared to photo-optical (0.5% versus 1.5%, P  =  .001). Nonetheless many photo-optical methods had very high precision and very low fail rates. CONCLUSIONS: Fibrinogen assays showed highly variable methodology and performance characteristics. Bias, precision, and grading were affected by the type of reagent or instrument used.

Clinical outcomes using a platelet function-guided approach for secondary prevention in patients with ischemic stroke or transient ischemic attack.

BACKGROUND AND PURPOSE: Antiplatelet therapy nonresponse is associated with worse clinical outcomes. We studied the clinical outcomes associated with platelet function-guided modifications in antiplatelet therapy in patients with ischemic stroke or transient ischemic attack. METHODS: From January 2005 to August 2007, 324 patients with ischemic stroke underwent platelet function testing using platelet aggregometry. Aspirin nonresponse was defined as a mean platelet aggregation ≥20% with 0.5 mg/mL arachidonic acid and/or ≥70% with 5 µmol/L adenosine diphosphate. Clopidogrel nonresponse was defined as a mean platelet aggregation ≥40% with 5 µmol/L adenosine diphosphate. A modification was any increase in antiplatelet therapy occurring after testing. Clinical outcomes were compared between patients with and without platelet function-guided antiplatelet therapy modifications using univariate and propensity score-adjusted analyses. RESULTS: In patients with ischemic stroke or transient ischemic attack, 43% (n=128) and 35% (n=54) were nonresponders to aspirin and clopidogrel, respectively. After platelet function testing, antiplatelet therapy was increased in 23% of patients (n=73). After propensity score matching (n=61 in each group), antiplatelet therapy modification was associated with significantly increased rates of death, ischemic events, or bleeding (hazard ratio, 2.24; 95% CI, 1.12-4.47; P=0.02) compared with no modification in antiplatelet therapy and a trend toward increased bleeding (hazard ratio, 3.56; 95% CI, 0.98-12.95; P=0.05). No differences in ischemic events were observed. CONCLUSIONS: Platelet function-guided modification in antiplatelet therapy after an ischemic stroke or transient ischemic attack was associated with significantly higher rates of adverse clinical outcomes.