(Circulation. 1999;99:620-625.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
Rapid Platelet-Function Assay
An Automated and Quantitative Cartridge-Based Method
From Accumetrics, Inc, San Diego, Calif (J.W.S., J.C., T.L., R.S.H.); the Department of Cardiology, Cleveland Clinic Foundation, Cleveland, Ohio (S.R.S., A.M.L.); and the Department of Medicine, Mount Sinai Medical Center, New York, NY (B.S.C.).
Correspondence to Dr Barry Coller, Department of Medicine, Box 1118, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029.
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Abstract |
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Background—The platelet glycoprotein (GP) IIb/IIIa receptor is important in mediating platelet thrombus formation, and the GP IIb/IIIa antagonist abciximab (c7E3 Fab; ReoPro) is effective in preventing thrombotic ischemic cardiovascular complications of unstable angina and percutaneous coronary interventions. Small-molecule antagonists of GP IIb/IIIa based on the Arg-Gly-Asp (RGD) sequence show similar benefit, and some of these agents are orally active. However, there may be significant interindividual variation in response to such antagonists, especially with chronic oral therapy. It will be essential to balance the beneficial antithrombotic effect of these drugs with their potential for causing bleeding. In response to this need, we have developed a rapid platelet-function assay (RPFA), a point-of-care system that provides a quantitative measure of the competence of the GP IIb/IIIa receptor as reflected in the ability of platelets to agglutinate fibrinogen-coated beads.
Methods and Results—Polystyrene beads were coated with fibrinogen and placed in a cartridge along with a lyophilized peptide that activates the thrombin receptor. Anticoagulated whole blood was added to the cartridge, and then a microprocessor-controlled operation mixed the reagents and detected agglutination between platelets and coated beads. Quantitative digital results were displayed within 3 minutes. Because there is no dilution of the blood, the assay can be used to measure platelet activity in samples that have been treated with GP IIb/IIIa antagonists with high dissociation rates. RPFA results of whole-blood samples treated with different GP IIb/IIIa antagonists correlated well with both conventional turbidimetric platelet aggregation (r2=0.95) and the percentage of free GP IIb/IIIa molecules in the sample (r2=0.96). The mean difference in measurements between RPFA and aggregometry was –4% (±4% SD), and the mean difference in measurements between RPFA and free GP IIb/IIIa receptors was –2% (±6% SD).
Conclusions—The RPFA provides rapid information on platelet function that mirrors turbidimetric platelet aggregation and reflects GP IIb/IIIa receptor blockade.
Key Words: platelets • glycoproteins • drugs
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Platelet glycoprotein (GP) IIb/IIIa receptor antagonists prevent ischemic complications of unstable angina and percutaneous coronary interventions. Data from the EPIC study using abciximab (c7E3 Fab; ReoPro) suggest the need to achieve and sustain for 12 hours
80%
blockade of GP IIb/IIIa receptors for significant
benefit.1 Results from studies with xemilofiban and
sibrafiban, oral antagonists of GP IIb/IIIa, however,
indicate that sustaining a similar level of inhibition of GP IIb/IIIa
for 
1 month can be associated with significant hemorrhagic
complications, some of which can be severe enough to require drug
withdrawal.2 3 4 Thus, to obtain optimal therapeutic
benefit during episodes of high thrombotic risk, it is important to
ensure that an adequate threshold of GP IIb/IIIa receptor blockade has
been achieved. For chronic therapy, however, to achieve the desired
antithrombotic benefit while avoiding unacceptable risk of
hemorrhage, it will most likely be desirable to achieve a
therapeutic window of GP IIb/IIIa receptor blockade analogous to the
strategy with oral anticoagulant therapy. A rapid and simple assay that
reflects the functional consequences of platelet GP IIb/IIIa
blockade might therefore be helpful in monitoring drug therapy and
perhaps guiding dose adjustments to achieve optimal benefit. Such an
assay may also be beneficial in monitoring patients after drug
withdrawal so as to know when platelet function has returned to
normal. We previously developed an assay sensitive to GP IIb/IIIa receptor blockade based on the ability of platelets in whole blood to agglutinate fibrinogen-coated beads when activated by a thrombin receptor–activating peptide.5 This assay, however, required the user to interpret a semiquantitative end- point. Here, we describe a microprocessor-controlled, whole-blood, cartridge-based, automated version of the assay that provides a quantitative digital display of the results within minutes. Results with this rapid platelet-function assay (RPFA) correlate well with results of traditional turbidimetric platelet aggregometry using citrated platelet-rich plasma (PRP) and radiometric binding assays of GP IIb/IIIa receptor occupancy.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Materials
Human fibrinogen (Enzyme Research Laboratories) was >95% pure, as judged by Coomassie blue staining of SDS polyacrylamide gels. Abciximab was the generous gift of Centocor (Malvern, Pa). [125I]NaI was purchased from Amersham. A modified thrombin receptor–activating peptide (iso-TRAP), iso-SFLLRN, which is resistant to plasma aminopeptidase M,5B was purchased from Multiple Peptide Systems. Vacutainer tubes containing 3.8% sodium citrate were obtained from Becton Dickinson. Polystyrene beads (
6 µm in diameter) with
surface carboxyl groups were purchased from Polysciences. Chemicals
used for buffers and assays were purchased from Sigma Chemical Co. The
GP IIb/IIIa antagonist TAK-029 was the generous gift of TAP
Holdings (Deerfield, Ill).
Fibrinogen Coating of Beads
Polystyrene beads are coated with fibrinogen by passive
adsorption and then dyed with an infrared (IR) dye to facilitate
measurements of bead agglutination in whole blood. A 3-step procedure
is used to make IR-dyed beads. First, fibrinogen (330 µg/mL) is
passively adsorbed to white polystyrene beads (6 µm in diameter)
in 20 mmol/L NaPO4, pH 7.5, for 2 hours at
room temperature. Unbound fibrinogen is removed by washing 3 times in
the same buffer. Protein assays indicate that 15% to 20% of the
total fibrinogen is coupled to the beads under these conditions. Then
the beads are dyed for 5 minutes with IR-140 (Aldrich) in 20
mmol/L NaPO4/methylene chloride/2-propanol
(1:4:6). The dye is removed and replaced with fresh dye in the same
solution for an additional 5 minutes. Finally, the beads are washed
extensively with 10 mmol/L HEPES, pH 7.5, containing 1 mg/mL of
BSA and 0.02% sodium azide. The absorbance properties and the ability
of the beads to be agglutinated are standardized for each lot of
beads.
Blood Collection and Preparation
For studies in which platelets were treated ex vivo with a
GP IIb/IIIa antagonist, human blood (40.5 mL) was collected
into 5-mL citrated Vacutainer tubes with a Vacutainer device and a
21-gauge needle. Blood was obtained from nonsmoking volunteers who had
not ingested aspirin for at least 3 days. The first tube was discarded,
and the remaining blood was pooled into a polypropylene container and
maintained at room temperature. A 1.5-mL sample of untreated blood was
removed for the RPFA, and the remainder was divided into 5-mL aliquots
and transferred to 12x75-mm polypropylene tubes. GP IIb/IIIa
antagonists were prepared in 10 mmol/L HEPES, 150
mmol/L NaCl, pH 7.4, and added to blood in a 1/10 volume to yield the
concentrations shown in the figure legends. A negative control was
prepared by adding 1/10 volume of 100 mmol/L EDTA to one of the
aliquots. Then, from each of the above tubes, 1.5 mL of whole blood was
removed and placed into separate polypropylene tubes for testing in the
RPFA. To obtain PRP for aggregometry, the remainder of the blood in the
tubes was centrifuged at 110g for 12 minutes at room
temperature. Platelet-poor plasma (PPP) was prepared by
centrifuging a separate aliquot of blood at 1540g for 15
minutes.
Patient data are from a protocol conducted at the Cleveland Clinic Foundation and approved by the Cleveland Clinic Foundation Institutional Review Board. Blood from patients undergoing elective percutaneous coronary interventions who were not treated with abciximab or other GP IIb/IIIa antagonists was collected into two 5-mL citrated Vacutainer tubes with a Vacutainer device and a 21-gauge needle. The first tube was discarded, and the remaining blood was used for the RPFA. All of the patients were taking aspirin, but none were on heparin or taking ticlopidine; 78% were male, 20% had recent myocardial infarctions, 61% had unstable angina, and 19% had stable angina. Separate blood samples were obtained for platelet count, mean platelet volume, and hematocrit.
Rapid Platelet-Function Assay
This assay is conducted in an integrated device, attached to a
personal computer, that houses a cylindrical warming chamber designed
to accommodate a 4.5-mL Vacutainer tube and a cartridge port to
accommodate a dual-channel cartridge (Figure 1
). The device also contains a light
source and optical detectors, as well as magnets to control mixing by
the steel balls in the reaction chambers. Each reaction chamber
contains lyophilized iso-TRAP and fibrinogen-coated beads. The assay is
initiated by addition of 160 µL of whole blood to each channel, which
reconstitutes the reagents such that the final iso-TRAP concentration
is 4 µmol/L. The sample is mixed back and forth by the movement
of the steel ball running the length of the sample chamber for 70
seconds, and the absorbance of the sample is measured 16 times per
second by the automated detector. Agglutination of fibrinogen-coated
beads by platelets is quantified by use of a microprocessor
algorithm that takes into account both the rate and extent of
agglutination. The data are reported as a rate of platelet function
in millivolts per 10 seconds (mV/10 s) ±95% CI based on goodness of
fit of the model to the data used to calculate the slope. The
instrument is programmed to reject the data (ie, a slope will not be
reported) if the interchannel variability is >15% or if the
intrachannel noise relative to the baseline is >7.5%. Experiments
were also conducted with cartridges containing ADP (20 µmol/L
final concentration) instead of iso-TRAP.
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Platelet Aggregometry
PRP (400 µL) was pipetted into a siliconized cuvette
containing a Teflon-coated stir bar. PPP was used to establish maximal
light transmission. The cuvette containing PRP was placed into a
Chrono-Log model 490D turbidimetric platelet aggregometer, and a
baseline tracing was established for 15 seconds. To stimulate
aggregation, ADP in 0.01 mol/L HEPES saline, 0.15 mol/L NaCl, pH 7.4,
was added to achieve a final concentration of 20 µmol/L.
Aggregation was monitored for 2 minutes, and the maximal aggregation
rate was recorded.
Binding of 125I-Abciximab to Platelets
Blockade of GP IIb/IIIa receptors on the platelet surface by
abciximab was assessed by use of a modification of our previously
described binding assay.5 Briefly, a 200-µL aliquot of
PRP prepared as above was incubated with 20 nmol/L
125I-abciximab for 10 minutes at 22°C. Then,
two 100-µL aliquots of the mixture were layered onto 30% sucrose
cushions and centrifuged at 12 000g for 3 minutes
at 22°C to pellet the platelets. Platelet pellets were
separated from the supernatant and counted in a gamma counter (Iso-Data
100). GP IIb/IIIa occupancy by abciximab was calculated by comparison
of the amount of 125I-abciximab bound to the
platelet surface in the presence of different concentrations of
unlabeled abciximab with the amount of
125I-abciximab bound to untreated
platelets.
Binding of 14C-TAK-029 to Platelets
TAK-029 is a small-molecule GP IIb/IIIa antagonist
patterned on the Arg-Gly-Asp (RGD) cell adhesion motif.6
It was also tested for its effects on platelet aggregometry and
RPFA, and the results were correlated with those obtained with an assay
to measure GP IIb/IIIa receptor occupancy by TAK-029.
14C-TAK-029, diluted with 10 mmol/L HEPES,
150 mmol/L NaCl, pH 7.4, was added to 200 µL of PRP to yield the
concentrations noted in the figure legends. After a 20-minute
incubation period, 100 µL of each mixture was placed into each of 2
polypropylene microcentrifuge tubes and centrifuged to
obtain platelet pellets. Each platelet pellet was subject to
scintillation counting in a Packard model 1500 Liquid Scintillation
Analyzer. Nonspecific binding was determined by competition
with a 300-fold excess of TAK-029. Specific binding of the compound was
then calculated by subtraction of nonspecific binding from the total
binding. The data were analyzed according to the method of
Scatchard.7
Statistical Analysis
Although correlation coefficients are commonly used to assess
the agreement between 2 methods, Bland and Altman8
demonstrated that this is statistically inappropriate, because the
correlation coefficient measures the strength of the relationship
between 2 variables, not the agreement between them. They proposed
a method that involves analyzing the differences between the methods
and assessing whether the differences are similar at all assay values.
The mean difference and the SD of the differences are valuable measures
that, when judged in the context of the medical significance of the
differences, allow one to assess the agreement between the methods. We
are reporting the data according to Bland and Altman as our primary
analysis. We are, however, also providing the correlation
coefficients to permit comparison of our data with those in the
literature.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Rapid Platelet-Function Assay
Mixing citrated whole blood with iso-TRAP and fibrinogen-coated beads in the cartridge reaction chamber results in progressive bead and platelet agglutination as the platelets interact with the fibrinogen-coated beads and with each other. This agglutination is detected as an increase in the transmission of infrared light through the sample (Figure 2A
). Both EDTA (Figure 2B) and abciximab 3 µg/mL (Figure 2C) prevent the
increase in transmission, indicating that the agglutination is divalent
cation– and GP IIb/IIIa–dependent, respectively.
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Day-to-Day and Cartridge Lot-to-Lot Variations in RPFA
Day-to-day variation in the RPFA of a single individual was
measured by testing 1 person's blood on 5 separate occasions over a
period of 5 months. The results (mean±SD) were 591±22 mV/10 s,
indicating relatively little variation. Five separate lots of
cartridges were used for this experiment, indicating that different
lots of cartridges give similar results.
RPFA Values of Patients Undergoing Coronary Intervention
In 50 patients presenting for elective
percutaneous coronary intervention, the
mean±SD values were 464±149 mV/10 s, with similar values for men
(578±20 mV/10 s, n=39) and women (478±142 mV/10 s, n=11). The rates
were not significantly correlated with donor platelet count
(r2=0.002), platelet density
(platelet count/1-hematocrit)
(r2=0.014), mean platelet volume
(r2=0.064), platelet mass
(platelet count x platelet volume)
(r2=0.16), or platelet mass
density (platelet mass/1-hematocrit)
(r2=0.014). The rates, however,
correlated moderately well with the inverse of the hematocrit
(r2=0.43). We suspect that this
relationship is most likely the result of the effect of the increased
absorbance of erythrocytes at higher hematocrits, but we cannot
rigorously exclude a potential effect of erythrocytes on platelet
function or rheology in the assay.
Comparison of the Effect of Abciximab and TAK-029 on GP IIb/IIIa
Receptor Blockade and Platelet Function Measured by RPFA and
Turbidimetric Aggregometry
The in vitro addition of increasing concentrations of abciximab to
citrated whole blood produced increasing inhibition of both the RPFA
and turbidimetric aggregometry (Figure 3). When normalized to baseline control
values, the percentage inhibition of the RPFA correlated well with both
the percentage inhibition of turbidimetric platelet aggregometry
and GP IIb/IIIa receptor blockade (Figure 3). In blood obtained
from 4 separate donors, the correlation between RPFA and turbidimetric
aggregometry was r2=0.98, and that
between RPFA and unblocked GP IIb/IIIa receptors was
r2=0.96 (Figure 4). The mean difference in measurements
between RPFA and aggregometry was –4%, and the SD of the differences
was 4%. The mean difference between RPFA and unblocked GP IIb/IIIa
receptors was –2%, and the SD of the differences was 6%.
IC50s determined on 4 separate patients with all
3 methods gave very similar results (Table 1). Moreover, the interindividual
differences in IC50s were small, differing from
the group means by <30%.
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) and by turbidimetric aggregometry
(
) were measured at each dose of abciximab. Occupancy of GP IIb/IIIa
receptors by abciximab (
) was also determined at each dose with
125I-abciximab. Results from each measurement are expressed
as percentage of baseline (untreated) value. This experiment is
representative of >20 such studies.
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An in vitro study was performed to assess the effect of aspirin on the ability of the RPFA to detect the effect of abciximab. Aspirin or buffer was added to the blood from 10 different volunteers (150 µmol/L final concentration), and then a 7-point abciximab dose-response curve was performed. The regression analysis comparing the 2 dose-response curves showed r2=0.97, demonstrating that aspirin did not diminish the sensitivity of RPFA to the effect of abciximab. Similarly, substituting heparin for citrate as the anticoagulant did not diminish the sensitivity of the RPFA to the effect of abciximab (r2=0.98).
TAK-029 was also tested for its ability to block GP IIb/IIIa receptors
and to inhibit platelet function measured by aggregometry and RPFA.
Our preliminary studies with TAK-029 and other low-molecular-weight
inhibitors of GP IIb/IIIa demonstrated that even modest
dilution of the blood sample immediately before testing resulted in an
underestimation of the degree of platelet-function inhibition
because the inhibitors dissociate from GP IIb/IIIa very
rapidly. To overcome this problem and to make the RPFA potentially
compatible with all GP IIb/IIIa antagonists, the reagents
and beads were lyophilized so that there is no dilution in the assay
beyond the anticoagulation step. Figure 5A shows the binding curve of
14C-TAK-029 to platelets, and Figure 5B shows the data expressed by the method of Scatchard,
indicating a Bmax of 137 000 molecules per
platelet and a KD of 37 to 42 nmol/L.
These data were then used to calculate the percentage of receptors
blocked by the different concentrations of TAK-029 in each sample
tested with the RPFA. The results shown in Figure 5C demonstrate
a close correlation (r2=0.92) between
the RPFA results and the GP IIb/IIIa receptor blockade assay. The mean
difference in measurement between the RPFA and GP IIb/IIIa receptor
blockade assay was –0.2%, and the SD of the differences was 8%.
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), nonspecific binding (
) of
14C-TAK-029 is shown. B, Scatchard analysis of data
to obtain affinity and number of binding sites per platelet.
Results from this analysis were then used to calculate
concentration of free (unoccupied) GP IIb/IIIa in each sample. C,
Correlation between free GP IIb/IIIa receptors and RPFA in blood
samples treated with different concentrations of TAK-029. This is 1 of
6 separate experiments, each of which used blood from different donors.
All experiments yielded similar results.
Comparison of ADP and iso-TRAP as Agonists in the RPFA
The RPFA results on blood obtained from 6 donors by use of
cartridges containing either lyophilized iso-TRAP or ADP 20
µmol/L are shown in Table 2. The
correlation between the values obtained with the different agonists was
very close (<3% difference for 4 donors, and 8% and 12% differences
for the other 2). The addition of abciximab to whole blood at
increasing doses resulted in progressive inhibition of RPFA values with
both the iso-TRAP and ADP cartridges
(r2=0.87) (Figure 6).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The RPFA measures platelet function using a small, undiluted sample of anticoagulated whole blood. The advantages of RPFA over other methods of assessing platelet function are (1) the speed with which results can be obtained, (2) the need for only a small sample of blood, (3) the semiautomated format in which processing of the blood is not required, (4) the microprocessor-controlled digital readout, and (5) its compatibility with a variety of anticoagulants and platelet agonists. The results from the RPFA can be reported as a percentage of baseline aggregation or as an absolute rate of aggregation. The results from the RPFA correlate well with results obtained from turbidimetric platelet aggregometry and with the percentage of free GP IIb/IIIa receptors. Thus, the mean differences between the assays range from –4% to 2%, and the SDs of the differences were 4% to 8%. The assay differs, however, from in vivo conditions in that it is not conducted under flowing conditions.
One potential use of the RPFA is to monitor GP IIb/IIIa receptor blockade by GP IIb/IIIa antagonists.9 It may, in fact, be applicable to both acute and chronic therapy. The dosing strategy with abciximab, which is administered as an intravenous bolus and 12-hour infusion, is to reach or exceed an 80% threshold of blockade and rely on the short exposure time to limit the hemorrhagic risk. Monitoring of abciximab treatment with RPFA may be beneficial in identifying unusual patients who do not obtain the desired response, for example, those with severe thrombocytosis,10 and ensuring that the blockade is sustained during the infusion; it may also be used to define when platelet function returns to baseline after therapy is completed. Chronic oral GP IIb/IIIa antagonist therapy may benefit from drug monitoring and dose adjustment because (1) the therapeutic window is likely to be relatively narrow, given the steepness of the dose-response curves, and (2) there are likely to be significant interindividual differences in bioavailability, pharmacokinetics, and functional effects, especially because renal and hepatic function may be variably compromised in the target population.9 It will be important, therefore, to assess the extent of interindividual variability in response to the agents, whether the variability correlates with outcome, and finally, whether dose adjustments made on the basis of the RPFA improve outcomes. Many other assays are being developed to monitor GP IIb/IIIa receptor blockade, some of which assess receptor blockade directly (reviewed in Reference 99 ). A functional assay such as the RPFA provides information on the total effect of the agents on platelet function, independent of the agent, and so provides a measure that is likely to be most biologically relevant. It can also be used when 2 different antagonists are present, as may occur during a transition from an intravenous agent to an oral agent.11
The RPFA may also be valuable in diagnosing the inherited platelet disorder Glanzmann thrombasthenia, because patients with this disorder lack functional GP IIb/IIIa receptors. Modifications to the RPFA with different agonists may also be useful to diagnose other platelet disorders or even to monitor the response of therapy with aspirin or other antiplatelet agents.
To further increase the automation of the RPFA, work is under way on a system that does not require an interface with a personal computer and that will require only the insertion of the Vacutainer tube into the cartridge. Finally, the cartridge will contain additional sample channels that can be formatted for other assays and to adjust for differences in optical properties among blood samples.
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Acknowledgments |
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This study was supported in part by grant 19278 from the National Heart, Lung, and Blood Institute. The authors would like to thank Boris Ratinov, Yen Ly, Susan Carette, and Divina Fernandez for their excellent technical support. We would also like to thank Suzanne Rivera for her excellent administrative support, Dr Kandice Kottke-Marchant at the Cleveland Clinic for assistance with measuring platelet function of cardiology patients, and Dr David Moliterno for his valuable comments.
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Footnotes |
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Dr Coller contributed to the design of the RPFA and the scientific review of this manuscript but did not participate in the collection of any of the clinical data or in the statistical analysis of the data. Dr Coller is an inventor of the RPFA, is on the Scientific Advisory Board of Accumetrics, and holds equity in Accumetrics, Inc. Dr Smith is a consultant to Accumetrics and holds equity in Accumetrics, Inc.
Received May 4, 1998; revision received September 23, 1998; accepted October 9, 1998.
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 V. L. Serebruany, A. I. Malinin, W. Ziai, A. N. Pokov, D. L. Bhatt, M. J. Alberts, and D. F. Hanley Effects of Clopidogrel and Aspirin in Combination Versus Aspirin Alone on Platelet Activation and Major Receptor Expression in Patients After Recent Ischemic Stroke: For the Plavix Use for Treatment of Stroke (PLUTO-Stroke) Trial Stroke, October 1, 2005; 36(10): 2289 - 2292. [Abstract] [Full Text] [PDF]
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P. Harrison, H. Segal, K. Blasbery, C. Furtado, L. Silver, and P. M. Rothwell Screening for Aspirin Responsiveness After Transient Ischemic Attack and Stroke: Comparison of 2 Point-of-Care Platelet Function Tests With Optical Aggregometry Stroke, May 1, 2005; 36(5): 1001 - 1005. [Abstract] [Full Text] [PDF]
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 V. L. Serebruany, M. G. Midei, A. I. Malinin, B. R. Oshrine, D. R. Lowry, D. C. Sane, J.-F. Tanguay, S. R. Steinhubl, P. B. Berger, C. M. O'Connor, et al. Absence of Interaction Between Atorvastatin or Other Statins and Clopidogrel: Results From the Interaction Study Arch Intern Med, October 11, 2004; 164(18): 2051 - 2057. [Abstract] [Full Text] [PDF]
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N. M.S.K.J. Ernst, H. Suryapranata, K. Miedema, R. J. Slingerland, J. P. Ottervanger, J. C.A. Hoorntje, A.T.M. Gosselink, J.-H. E. Dambrink, M.-J. de Boer, F. Zijlstra, et al. Achieved platelet aggregation inhibition after different antiplatelet regimens during percutaneous coronary intervention for ST-segment elevation myocardial infarction J. Am. Coll. Cardiol., September 15, 2004; 44(6): 1187 - 1193. [Abstract] [Full Text] [PDF]
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E. I. Lev, D. Hasdai, E. Scapa, A. Tobar, A. Assali, J. Lahav, A. Battler, J. J. Badimon, and R. Kornowski Administration of eptifibatide to acute coronary syndrome patients receiving enoxaparin or unfractionated heparin: Effect on platelet function and thrombus formation J. Am. Coll. Cardiol., March 17, 2004; 43(6): 966 - 971. [Abstract] [Full Text] [PDF]
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 R. A. Reiter, F. Mayr, H. Blazicek, E. Galehr, P. Jilma-Stohlawetz, H. Domanovits, and B. Jilma Desmopressin antagonizes the in vitro platelet dysfunction induced by GPIIb/IIIa inhibitors and aspirin Blood, December 15, 2003; 102(13): 4594 - 4599. [Abstract] [Full Text] [PDF]
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W. C. Lau, L. A. Waskell, P. B. Watkins, C. J. Neer, K. Horowitz, A. S. Hopp, A. R. Tait, D. G.M. Carville, K. E. Guyer, and E. R. Bates Atorvastatin Reduces the Ability of Clopidogrel to Inhibit Platelet Aggregation: A New Drug-Drug Interaction Circulation, January 7, 2003; 107(1): 32 - 37. [Abstract] [Full Text] [PDF]
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A. W. Bonz, B. Lengenfelder, J.o. Strotmann, S. Held, O. Turschner, K. Harre, C. Wacker, C. Waller, N. Kochsiek, M. Meesmann, et al. effect of additional temporary glycoprotein IIb/IIIa receptor inhibition on troponin release in elective percutaneous coronary interventions after pretreatment with aspirin and clopidogrel (TOPSTAR trial) J. Am. Coll. Cardiol., August 21, 2002; 40(4): 662 - 668. [Abstract] [Full Text] [PDF]
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T. Palmerini, M. A. Nedelman, L. E. Scudder, M. T. Nakada, R. E. Jordan, S. Smyth, R. E. Gordon, J. T. Fallon, and B. S. Coller Effects of abciximab on the acute pathology of blood vessels after arterial stenting in nonhuman primates J. Am. Coll. Cardiol., July 17, 2002; 40(2): 360 - 366. [Abstract] [Full Text] [PDF]
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F.W.G. Leebeek, E. Boersma, C.P. Cannon, F.J.J. van de Werf, and M.L. Simoons Oral glycoprotein IIb/IIIa receptor inhibitors in patients with cardiovascular disease: why were the results so unfavourable Eur. Heart J., March 2, 2002; 23(6): 444 - 457. [Full Text] [PDF]
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S. Samson and L. Shore-Lesserson Platelet Function and Cardiopulmonary Bypass Seminars in Cardiothoracic and Vascular Anesthesia, November 1, 2001; 5(4): 273 - 281. [Abstract] [PDF]
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L. Shore-Lesserson Monitoring the Hematologic Complications of Cardiopulmonary Bypass Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2001; 5(3): 207 - 216. [Abstract] [PDF]
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S. R. Steinhubl, J. D. Talley, G. A. Braden, J. E. Tcheng, P. J. Casterella, D. J. Moliterno, F. I. Navetta, P. B. Berger, J. J. Popma, G. Dangas, et al. Point-of-Care Measured Platelet Inhibition Correlates With a Reduced Risk of an Adverse Cardiac Event After Percutaneous Coronary Intervention : Results of the GOLD (AU-Assessing Ultegra) Multicenter Study Circulation, May 29, 2001; 103(21): 2572 - 2578. [Abstract] [Full Text] [PDF]
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F.-J. Neumann, W. Hochholzer, G. Pogatsa-Murray, A. Schomig, and M. Gawaz Antiplatelet effects of abciximab, tirofiban and eptifibatide in patients undergoing coronary stenting J. Am. Coll. Cardiol., April 1, 2001; 37(5): 1323 - 1328. [Abstract] [Full Text] [PDF]
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J. I. Osende, V. Fuster, E. I. Lev, D. Shimbo, U. Rauch, J. D. Marmur, M. Richard, D. Varon, and J. J. Badimon Testing Platelet Activation With a Shear-Dependent Platelet Function Test Versus Aggregation-Based Tests : Relevance for Monitoring Long-Term Glycoprotein IIb/IIIa Inhibition Circulation, March 20, 2001; 103(11): 1488 - 1491. [Abstract] [Full Text] [PDF]
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K. M. Akkerhuis, K.-L. Neuhaus, R. G. Wilcox, A. Vahanian, J.-L. Boland, J. Hoffmann, T. Baardman, G. Nehmiz, U. Roth, A. P. J. Klootwijk, et al. Safety and preliminary efficacy of one month glycoprotein IIb/IIIa inhibition with lefradafiban in patients with acute coronary syndromes without ST-elevation A phase II study Eur. Heart J., December 2, 2000; 21(24): 2042 - 2055. [Abstract] [PDF]
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 D. L. Bhatt and E. J. Topol Current Role of Platelet Glycoprotein IIb/IIIa Inhibitors in Acute Coronary Syndromes JAMA, September 27, 2000; 284(12): 1549 - 1558. [Abstract] [Full Text] [PDF]
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K. Peter, B. Kohler, A. Straub, J. Ruef, M. Moser, T. Nordt, M. Olschewski, M. E. Ohman, W. Kubler, and C. Bode Flow Cytometric Monitoring of Glycoprotein IIb/IIIa Blockade and Platelet Function in Patients With Acute Myocardial Infarction Receiving Reteplase, Abciximab, and Ticlopidine : Continuous Platelet Inhibition by the Combination of Abciximab and Ticlopidine Circulation, September 26, 2000; 102(13): 1490 - 1496. [Abstract] [Full Text] [PDF]
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 G. J. Despotis and L. T. Goodnough Management approaches to platelet-related microvascular bleeding in cardiothoracic surgery Ann. Thorac. Surg., August 1, 2000; 70(2): S20 - 32. [Abstract] [Full Text] [PDF]
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 J. B. Bussel, T. J. Kunicki, and A. D. Michelson Platelets: New Understanding of Platelet Glycoproteins and Their Role in Disease Hematology, January 1, 2000; 2000(1): 222 - 240. [Abstract] [Full Text] [PDF]
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T. A. Waldmann, R. Levy, and B. S. Coller Emerging Therapies: Spectrum of Applications of Monoclonal Antibody Therapy Hematology, January 1, 2000; 2000(1): 394 - 408. [Abstract] [Full Text] [PDF]
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 A. T. Nurden, C. Poujol, C. Durrieu-Jais, and P. Nurden Platelet Glycoprotein IIb/IIIa Inhibitors : Basic and Clinical Aspects Arterioscler Thromb Vasc Biol, December 1, 1999; 19(12): 2835 - 2840. [Full Text] [PDF]
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S. R. Steinhubl, K. Kottke-Marchant, D. J. Moliterno, M. L. Rosenthal, N. K. Godfrey, B. S. Coller, E. J. Topol, and A. M. Lincoff Attainment and Maintenance of Platelet Inhibition Through Standard Dosing of Abciximab in Diabetic and Nondiabetic Patients Undergoing Percutaneous Coronary Intervention Circulation, November 9, 1999; 100(19): 1977 - 1982. [Abstract] [Full Text] [PDF]
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