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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
From the Free Radical Biology & Aging Research Program,
Oklahoma Medical Research Foundation, Oklahoma City; the Coagulation
Service and Thrombosis Research Unit, Scientific Institute HS Raffaele,
Milan, Italy; and Serbio (Diagnostica Stago), Gennevilliers, France.
The endothelial protein C receptor (EPCR) facilitates protein C
activation and plays a protective role in the response to Escherichia coli-mediated sepsis in primates. Previously,
a soluble form of EPCR (sEPCR) in human plasma was characterized, and
several studies indicated that generation of sEPCR is regulated by
inflammatory mediators, including thrombin-mediated up-regulation of
surface metalloproteolytic activity in vitro. This study addressed the question of whether plasma sEPCR levels reflect changes in thrombin generation in patients undergoing anticoagulant treatment. The sEPCR
levels in patients treated with coumarin-type oral anticoagulants were
significantly lower than those in healthy asymptomatic adult volunteers
(105.3 ± 70.8 ng/mL [n = 55] versus 165.8 ± 115.8 ng/mL [n = 200]; P < .0001). A similar decline in plasma
sEPCR levels was found in patients treated with unfractionated heparin.
In healthy volunteers, sEPCR levels declined to about 100 ng/mL within 3 days after initiation of an 8-day period of warfarin administration and increased within 2 days after its cessation. Plasma sEPCR levels
returned to pretreatment values within 1 week, and the changes in
plasma sEPCR levels mirrored changes in values for international
normalized ratios. A similar decline in sEPCR levels with time was
observed in 7 patients beginning treatment with warfarin for a
thrombotic disorder. Prothrombin fragment 1 + 2 levels also decreased
in volunteers and patients given warfarin. These results show that
plasma sEPCR levels decline in response to treatment with
anticoagulants whose mechanism of action is known to decrease in vivo
thrombin production.
(Blood. 2002;99:526-530) Perturbations of hemostasis are central to
the pathogenesis of a hypercoagulable state and may be triggered by
multiple, overlapping influences. These include but are not limited to
environmental effects (surgery, diet, smoking, childbirth, and trauma),
manifestations of a primary disease (cardiovascular or cerebrovascular
disease, diabetes, sepsis, hypertension, autoimmune disease, and
malignant disease), or inheritable defects in hemostatic factors
(protein C, protein S, factor V Leiden, prothrombin, and
antithrombin).1-3
Currently, the therapeutic approach for patients with thrombotic
disease typically starts with an intravenous course of unfractionated heparin or low-molecular-weight heparin, followed by a course of oral
anticoagulation. In North America and Europe, warfarin (4-hydroxycoumarin) and other coumarin derivatives are the most widely
used oral anticoagulants for preventing and treating venous or arterial
thrombosis and embolism. The basic premise of anticoagulant therapy is
that it will ultimately reduce formation of thrombin by interfering
with the vitamin K-dependent coagulation factors required for
activation of prothrombin.4,5 Thrombin is the final enzyme
product of the coagulation cascade and is needed to form fibrin and to
activate platelets, both of which are essential components of a clot.
Thrombin is also needed for the protein C anticoagulant regulatory
system to function properly. The protein C system is a primary
regulatory pathway of coagulation and thrombin formation.6 The activated protein C generated by this pathway inactivates critical
coagulation factors required for thrombin formation. An endothelial
protein C receptor (EPCR) has been identified7,8 and shown
to facilitate the protein C activation by the thrombin/thrombomodulin system.9 Immunohistochemistry studies found that
membrane-bound EPCR is expressed on endothelial cells, with increasing
expression corresponding to increasing vessel
diameter.10,11 A soluble form of EPCR (sEPCR) exists in
plasma, and retains its ability to bind both protein C zymogen and
activated protein C, although it cannot augment protein C
activation.12 Recently it was shown that recombinant sEPCR
binds to activated neutrophils partly by means of proteinase 3, a
neutrophil granule serine proteinase, and may be involved in modulating
autoantibody-mediated neutrophil inflammatory events.13
Previous studies found that sEPCR is generated in vitro from its
endothelial-bound parent by metalloproteinase activity, and this
activity is inducible by thrombin and inflammatory
mediators.14 In an in vivo rodent model of sepsis,
up-regulation of EPCR messenger RNA (mRNA) and sEPCR generation by
thrombin infusion was inhibited by hirudin.15 Furthermore,
the murine EPCR gene contains a thrombin response element, and
expression of a transgene driven by the murine EPCR promoter was found
to be responsive to thrombin.16 Although the physiologic
importance of sEPCR in vivo is unknown, elevated sEPCR levels are found
in patients with sepsis and systemic lupus erythematosus, conditions
associated with considerable thrombin production and
coagulopathy.17 In this study, we addressed the question
of whether plasma sEPCR levels are related to thrombin production in
vivo by evaluating the effect of anticoagulant administration on
circulating sEPCR levels in patients and healthy volunteers.
Patients and volunteers
Six healthy Italian volunteers (3 men and 3 women; mean age ± SD;
38 ± 11 years) agreed to undergo an 8-day course of warfarin administration. All received an initial dose of 10 mg/day, which was
then adjusted on the basis of international normalized ratio (INR)
results, aiming for a target of 2.5. Blood samples were obtained at
11:00 AM from an antecubital vein 2 days before the first
dose of warfarin and 24 hours after the intake of warfarin for the
first 5 days. Blood samples were also collected on days 8 through 12 and on day 15. To monitor changes in thrombin production, levels of
prothrombin fragment 1 + 2 (F1 + 2) were measured with a commercial
enzyme-linked immunosorbent assay (ELISA; Enzygnost F1 + 2;
Dade-Behring, Milan, Italy). Plasma protein C antigen was measured by
Laurell rocket immunoelectrophoresis using purified goat antihuman
protein C IgG.18
Blood samples were collected from 10 Italian patients (5 men and 5 women; mean age, 70 ± 5 years) treated for at least 2 days with
therapeutic dosages of intravenous unfractionated sodium heparin (mean
activated partial thromboplastin time [APTT] ratio, 2.65 ± 0.89)
because of unstable angina, myocardial infarction (n = 5), or venous
thromboembolism (n = 5). Samples were also collected from 7 additional patients (3 men and 4 women; mean age, 71 ± 13 years)
before and at different times after initiation of warfarin treatment
(without previous heparin therapy) for atrial fibrillation (n = 4),
dilative cardiomyopathy, mitral valve disease, or deep vein thrombosis.
All blood samples (4.5 mL) were collected in Vacutainer tubes
containing 0.5 mL 0.129 M trisodium citrate (Becton Dickinson,
Plymouth, United Kingdom). Platelet-poor plasma was obtained within 2 hours by centrifugation at room temperature for 10 minutes at
1500g. INR (Hemoliance Recombiplastin) and APTT (STA PTTA;
Diagnostica Stago, Gennevilliers, France) determinations were done in
samples of fresh plasma. The remaining plasma was divided into aliquots
in Eppendorf tubes (0.4 mL), snap-frozen with methanol and dry ice, and
stored at Assay of plasma sEPCR levels
It was found previously that sEPCR is generated from its
endothelial-bound parent in vitro by metalloproteinase activity induced by thrombin and some inflammatory mediators,14 thus
raising the question of whether sEPCR levels in plasma may reflect in vivo thrombin generation. To address this question, we determined sEPCR
levels in patients receiving vitamin K-antagonist oral anticoagulant therapy and compared those with sEPCR levels in an apparently healthy
adult population. Because the effect, if any, of diet or other
environmental factors on plasma sEPCR levels is unknown, data from
patient samples were compared with data from healthy adult samples
obtained from the same geographic region. A French population of
patients receiving oral anticoagulant therapy with acenocoumarol,
fluindione, or warfarin had significantly lower sEPCR levels
(105.3 ± 70.8 ng/mL; n = 55) than a healthy French population
(165.8 ± 115.8 ng/mL [range, 57.8-693.5 ng/mL]; n = 200;
P < .0001; Figure 1A). In
the healthy population, sEPCR levels tended to be higher in the men
than in the women (184.51 ± 129.2 ng/mL [n = 100] versus
147.1 ± 97.8 ng/mL [n = 100]; P < .01). Additional
analysis of data from the healthy population revealed a bimodal
distribution in which the majority of volunteers had plasma sEPCR
levels of approximately 75 to 175 ng/mL, but about 20% had much higher
levels (up to nearly 700 ng/mL).
To evaluate the relation between plasma sEPCR levels and anticoagulant therapy further, samples were obtained from Italian patients undergoing intravenous unfractionated heparin therapy. Samples from an apparently healthy Italian adult population had a mean sEPCR level of 195.1 ± 114.0 ng/mL (n = 49; Figure 1B), a value that did not differ significantly from that in the healthy French population. In addition, a similar bimodal distribution was observed. Patients receiving intravenous heparin therapy had lower sEPCR levels (147.1 ± 39.3 ng/mL [n = 10]; P < .09) than the healthy volunteers (Figure 1B). Although the number of samples from patients receiving heparin therapy was small, the reduction in plasma sEPCR levels followed the trend observed in patients undergoing oral anticoagulant therapy with vitamin K antagonists. The effect of warfarin treatment on plasma sEPCR levels in healthy
adults was studied in 6 volunteers (Figure
2A). The volunteers received warfarin
(oral anticoagulation) for 8 days, and follow-up was extended to day 15 after the beginning of warfarin administration. Blood for evaluation of
INR levels was obtained before the warfarin regimen began (day 0) and
on each day of the 15 days of the study. The warfarin dosage was
adjusted as needed for each subject based on the subject's daily INR
value. As shown in Figure 2A, plasma sEPCR levels declined during
warfarin administration. There was a lag time of 24 to 48 hours before
sEPCR levels decreased, and the extent of the decline varied among the
volunteers. Approximately 24 to 48 hours after cessation of warfarin
administration, sEPCR levels began to increase in all volunteers, with
most reaching pretreatment values by day 15. The INR values in the
samples from these volunteers were essentially a mirror image of the
sEPCR levels (Figure 2B).
To confirm that administration of warfarin is accompanied by a decrease in thrombin production in healthy individuals, F1 + 2 levels were monitored (Figure 2C). Levels of F1 + 2 decreased as a result of the warfarin administration, with a significant decrease observed on day 5 (to 39% of initial values; P < .05). The F1 + 2 levels appeared to return to pretreatment levels more slowly than did the sEPCR levels. Table 1 shows the changes in sEPCR and
protein C antigen values in the 6 healthy volunteers given warfarin.
The data are expressed as percent variations relative to baseline
values (day 0), with the corresponding INR values. A significant
decrease in sEPCR levels was first observed on day 3 (to 77% of
initial values; P < .05), and this persisted until about
48 hours after the last warfarin administration. Protein C antigen
levels dropped rapidly, to 46% of baseline values by day 2, and
returned to normal levels 96 hours after the last warfarin
administration. In a previous study of volunteers given an 8-day
warfarin regimen, factor II levels reached a nadir more slowly (between
days 2 and 5) than other vitamin K-dependent coagulation factors,
after which F1 + 2 levels declined.20 Thus, in healthy
volunteers, prevention of prothrombin activation by warfarin was not
observed until after a significant drop in factor II levels, coinciding
with the reductions in sEPCR and F1 + 2 levels observed in the
current study. Together, these data suggest that the decrease in sEPCR
is not dependent on reduced circulating levels of protein C but rather
mirrors the inhibition of in vivo thrombin generation.
A similar reduction in sEPCR values with time was observed in patients
beginning therapy with oral anticoagulants. Blood was obtained before
the start of anticoagulation, and sEPCR levels (Figure
3A) and F1 + 2 levels (Figure 3B) were
determined during the course of therapy. In all patients studied, sEPCR
levels declined with time after the start of oral anticoagulant
therapy, and as was also observed in healthy volunteers, the extent of
the decrease varied. As expected, F1 + 2 levels declined in most of
the patients after initiation of warfarin therapy, particularly in
those with higher prothrombin fragment levels (Figure 3C).
The current results indicate that anticoagulant therapy not only reduces thrombin generation but also decreases plasma sEPCR levels. Patients undergoing anticoagulant therapy with oral vitamin K antagonists (acenocoumarol, fluindione, or warfarin) or intravenous unfractionated heparin had lower sEPCR plasma levels than populations of healthy volunteers. In both the patients and the healthy volunteers given warfarin, the time frame for the changes in sEPCR levels also coincided with the known changes in vitamin K-dependent factors induced by warfarin.5,18,20,21 On initiation of warfarin administration, there was a delay of 2 to 3 days before sEPCR levels declined. Subsequently, when warfarin administration to the healthy volunteers ended after 8 days, plasma sEPCR levels began to rise by day 10 to 11 and, in most cases, reached pretreatment levels within a week after warfarin administration ended. Rather than paralleling the changes in protein C antigen levels, the changes in sEPCR mirrored the changes in INR values. Plasma F1 + 2 levels also declined with warfarin administration in both the volunteers and the patients, a finding that supports the idea that thrombin production decreased. However, the kinetics of the changes in F1 + 2 levels and sEPCR levels with warfarin administration did not coincide entirely in the healthy volunteers. We observed that sEPCR levels responded more rapidly to the start and cessation of warfarin administration. The in vivo pharmacokinetics of sEPCR has not been studied, but the vast difference between the modes of production and/or plasma clearance of the 2 markers may contribute to this observation. This responsiveness of plasma sEPCR levels to anticoagulant therapy is consistent with the current model for generation of sEPCR from endothelial cells. Studies in cultured cells or in a rat sepsis model suggested that EPCR mRNA and ectodomain shedding into the circulation are responsive to thrombin activity, probably as an indirect result of thrombin-induced metalloproteinase activity.14-16 The current study does present the mechanism of sEPCR formation in humans, but it did have the novel finding that changes in plasma sEPCR levels in both patients and healthy volunteers can be induced by anticoagulant treatment. The effect of anticoagulant treatment was not absolute, however, in that sEPCR levels never approached zero but tended to stabilize at about 100 ng/mL in healthy volunteers and at somewhat higher levels in patients (Figures 2 and 3). Thus, there may be an alternative pathway of sEPCR production that is independent of thrombin. We also cannot rule out the possibility that a downstream product of thrombin activity (eg, plasmin) contributes to changes in sEPCR levels. However, the observation that sEPCR levels declined with administration of either warfarin or unfractionated heparin, which have distinctly different mechanisms for inhibiting thrombin formation, suggests that the reduction in plasma sEPCR levels was directly related to a reduction in thrombin generation. Earlier studies showed that plasma sEPCR is functional, at least with respect to its ability to bind protein C and activated protein C.12 Thus, it differs from soluble thrombomodulin, which is proteolyzed by neutrophil elastase and cathepsin G at the endothelial surface to release a variety of degraded forms into the circulation.22 Because the mechanisms for release of these 2 endothelial-derived proteins differ considerably, the plasma levels of these soluble receptors may be reporting different facets of endothelial status during a pathologic process. Soluble thrombomodulin is an accepted marker for endothelial damage, having been shown to be elevated in a variety of disease states with histological evidence of endothelial damage.23-25 It is possible that soluble thrombomodulin levels reflect endothelial damage, whereas soluble EPCR levels monitor an endothelial response to injury. This idea is consistent with the observation that plasma sEPCR levels, but not soluble thrombomodulin levels, are related to disease activity in patients with Wegener granulomatosis, an autoimmune vasculitis characterized by activation of both immune and coagulation systems (manuscript submitted, October 2001). There are several ways to evaluate thrombin generation, including assessment of enzymatic activity,26 or the more common measurements of plasma thrombin-antithrombin complexes, F1 + 2, and D-dimer used clinically.1 Clinical evaluation of a patient's prothrombotic status and the efficacy of an anticoagulant therapy regimen takes into account the levels of these markers as well as the integrity of coagulation-pathway members and inhibitors by means of plasma thromboplastin (PT) and APTT clotting assays. Each of these approaches involves technical difficulties, including thrombin generation during phlebotomy and standardization of test reagents (INR).27 The PT clotting assay is the most useful screening method, yet it is more sensitive to agents or events that result in prolongation of the clotting times. There is a good correlation between prolonged PT times and bleeding episodes in patients undergoing anticoagulant therapy. However, it can be difficult to detect underdosing of anticoagulant therapy by assessment of PT and INR values. Long-term inadequate treatment maintains a hypercoagulable state, so patients unknowingly remain at risk for thrombotic events.28 The current observation that sEPCR levels decrease in response to anticoagulant therapy suggests that sEPCR may have potential as a marker of thrombin generation. Given the probable mode of generation of sEPCR and its assay method, measurement of plasma sEPCR levels would most likely not be affected by the technical difficulties associated with current tests of thrombin generation. Related to this notion is the observation that there appear to be 2 subpopulations within the apparently healthy population in terms of sEPCR levels. In both the French and the Italian volunteers we studied, most had sEPCR levels in the range of 75 to 175 ng/mL (Figure 1). The rest had levels scattered in the range of 200 to 700 ng/mL. Although we cannot rule out an effect of environmental (smoking and diet) or genetic (polymorphisms and sex) factors, the observation that sEPCR levels fell in healthy volunteers during warfarin administration suggests that those with exceedingly high sEPCR levels may have had higher levels of endogenous thrombin production. This observation suggests that sEPCR levels may be a marker for a hypercoagulable state. However, more studies in a variety of populations are necessary to support this speculation. In summary, our findings demonstrate a relation between plasma sEPCR levels and thrombin generation in healthy volunteers and in patients undergoing anticoagulant therapy. We anticipate that additional studies, particularly those examining different thrombin inhibitors, will provide insight into the potential usefulness of plasma sEPCR levels in evaluating a hypercoagulable state.
Submitted June 15, 2001; accepted September 14, 2001.
Supported by an Initial Investigator Award (D.J.S.-K.) and a Scientist Development Grant (S.K.) from the American Heart Association; grants from the National Institutes of Health (HL64787 and AI47575 to S.K.) and Telethon-Italy (A.D.); and research funding from Diagnostica Stago (N.C., M.G., and B.W.)
N.C., M.G., and B.W. are employed by Diagnostica Stago whose product was studied in the present work.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Shinichiro Kurosawa, Free Radical Biology & Aging Research Program, Oklahoma Medical Research Foundation, 825 NE 13th St, Oklahoma City, OK 73104; e-mail: kurosawas{at}omrf.ouhsc.edu.
1. Carey MJ, Rodgers GM. Disseminated intravascular coagulation: clinical and laboratory aspects. Am J Hematol. 1998;59:65-73[CrossRef][Medline] [Order article via Infotrieve]. 2. Kearon C, Crowther M, Hirsh J. Management of patients with hereditary hypercoagulable disorders. Annu Rev Med. 2000;51:169-185[CrossRef][Medline] [Order article via Infotrieve].
3.
Lane DA, Grant PJ.
Role of hemostatic gene polymorphisms in venous and arterial thrombotic disease.
Blood.
2000;95:1517-1532
4.
Hirsh J, Dalen JE, Anderson DR, et al.
Oral anticoagulants: mechanism of action, clinical effectiveness, and optimal therapeutic range.
Chest.
1998;114:445S-469S 5. Breckenridge A. Oral anticoagulant drugs: pharmacokinetic aspects. Semin Hematol. 1978;15:19-26[Medline] [Order article via Infotrieve].
6.
Esmon CT, Gu JM, Xu J, Qu D, Stearns-Kurosawa DJ, Kurosawa S.
Regulation and functions of the protein C anticoagulant pathway.
Haematologica.
1999;84:363-368
7.
Fukudome K, Esmon CT.
Molecular cloning and expression of murine and bovine endothelial cell protein C/activated protein C receptor (EPCR): the structural and functional conservation in human, bovine, and murine EPCR.
J Biol Chem.
1995;270:5571-5577
8.
Fukudome K, Esmon CT.
Identification, cloning, and regulation of a novel endothelial cell protein C/activated protein C receptor.
J Biol Chem.
1994;269:26486-26491
9.
Stearns-Kurosawa DJ, Kurosawa S, Mollica JS, Ferrell GL, Esmon CT.
The endothelial cell protein C receptor augments protein C activation by the thrombin-thrombomodulin complex.
Proc Natl Acad Sci U S A.
1996;93:10212-10216
10.
Laszik Z, Mitro A, Taylor FB Jr, Ferrell G, Esmon CT.
Human protein C receptor is present primarily on endothelium of large blood vessels: implications for the control of the protein C pathway.
Circulation.
1997;96:3633-3640 11. Ye X, Fukudome K, Tsuneyoshi N, et al. The endothelial cell protein C receptor (EPCR) functions as a primary receptor for protein C activation on endothelial cells in arteries, veins, and capillaries. Biochem Biophys Res Commun. 1999;259:671-677[CrossRef][Medline] [Order article via Infotrieve]. 12. Kurosawa S, Stearns-Kurosawa DJ, Hidari N, Esmon CT. Identification of functional endothelial protein C receptor in human plasma. J Clin Invest. 1997;100:411-418[Medline] [Order article via Infotrieve].
13.
Kurosawa S, Esmon CT, Stearns-Kurosawa DJ.
The soluble endothelial protein C receptor binds to activated neutrophils: involvement of proteinase-3 and CD11b/CD18.
J Immunol.
2000;165:4697-4703
14.
Xu J, Qu D, Esmon NL, Esmon CT.
Metalloproteolytic release of endothelial protein C receptor.
J Biol Chem.
2000;275:6038-6044
15.
Gu JM, Katsuura Y, Ferrell GL, Grammas P, Esmon CT.
Endotoxin and thrombin elevate rodent endothelial cell protein C receptor mRNA levels and increase receptor shedding in vivo.
Blood.
2000;95:1687-1693
16.
Gu JM, Fukudome K, Esmon CT.
Characterization and regulation of the 5'-flanking region of the murine endothelial protein C receptor gene.
J Biol Chem.
2000;275:12481-12488
17.
Kurosawa S, Stearns-Kurosawa DJ, Carson CW, D'Angelo A, Della VP, Esmon CT.
Plasma levels of endothelial cell protein C receptor are elevated in patients with sepsis and systemic lupus erythematosus: lack of correlation with thrombomodulin suggests involvement of different pathological processes.
Blood.
1998;91:725-727 18. Vigano D'Angelo S, Comp PC, Esmon CT, D'Angelo A. Relationship between protein C antigen and anticoagulant activity during oral anticoagulation and in selected disease states. J Clin Invest. 1986;77:416-425.
19.
Fukudome K, Kurosawa S, Stearns-Kurosawa DJ, He X, Rezaie AR, Esmon CT.
The endothelial cell protein C receptor: cell surface expression and direct ligand binding by the soluble receptor.
J Biol Chem.
1996;271:17491-17498 20. D'Angelo A, Della Valle P, Cripa L, Mazzola G, Agazzi A, Vigano-D'Angelo S. Effective warfarin-dependent inhibition of prothrombin activation occurs after the reduction of plasma factor II [abstract]. Thromb Haemost. 1993;69:1132. 21. Sutcliffe FA, MacNicoll AD, Gibson GG. Aspects of anticoagulant action: a review of the pharmacology, metabolism and toxicology of warfarin and congeners. Rev Drug Metab Drug Interact. 1987;5:225-272[Medline] [Order article via Infotrieve]. 22. Abe H, Okajima K, Okabe H, Takatsuki K, Binder BR. Granulocyte proteases and hydrogen peroxide synergistically inactivate thrombomodulin of endothelial cells in vitro. J Lab Clin Med. 1994;123:874-881[Medline] [Order article via Infotrieve].
23.
Takano S, Kimura S, Ohdama S, Aoki N.
Plasma thrombomodulin in health and diseases.
Blood.
1990;76:2024-2029 24. Takahashi H, Ito S, Hanano M, Wada K, Niwano H, Seki Y, Shibata A. Circulating thrombomodulin as a novel endothelial cell marker: comparison of its behavior with von Willebrand factor and tissue-type plasminogen activator. Am J Hematol. 1992;41:32-39[Medline] [Order article via Infotrieve]. 25. Boffa MC, Karmochkine M. Thrombomodulin: an overview and potential implications in vascular disorders. Lupus. 1998;7(suppl 2):S120-S125. 26. Hemker HC, Giesen PLA, Ramjee M, Wagenvoord, Beguin S. The thrombogram: monitoring thrombin generation in platelet rich plasma. Thromb Haemost. 2000;83:589-591[Medline] [Order article via Infotrieve]. 27. Riley RS, Rowe D, Fisher LM. Clinical utilization of the international normalized ratio (INR). J Clin Lab Anal. 2000;14:101-114[CrossRef][Medline] [Order article via Infotrieve]. 28. Schaufele MK, Marciello MA, Burke DT. Dosing practices of physicians for anticoagulation with warfarin during inpatient rehabilitation. Am J Phys Med Rehabil. 2000;79:69-74[CrossRef][Medline] [Order article via Infotrieve].
© 2002 by The American Society of Hematology.
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  B. Saposnik, J.-L. Reny, P. Gaussem, J. Emmerich, M. Aiach, and S. Gandrille A haplotype of the EPCR gene is associated with increased plasma levels of sEPCR and is a candidate risk factor for thrombosis Blood, February 15, 2004; 103(4): 1311 - 1318. [Abstract] [Full Text] [PDF]
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M. J. A. Simmelink, P. G. de Groot, R. H. W. M. Derksen, J. A. Fernandez, and J. H. Griffin Oral anticoagulation reduces activated protein C less than protein C and other vitamin K-dependent clotting factors Blood, December 1, 2002; 100(12): 4232 - 4233. [Abstract] [Full Text] [PDF]
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Top
Abstract
Introduction
70°C until testing. Plasma
samples were obtained from patients undergoing vitamin K-antagonist
oral anticoagulant therapy with acenocoumarol, fluindione, or warfarin
and recruited at a French general hospital (Assistance Hôpitaux
Publique de Paris, France). All samples were obtained with informed consent.
