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INTRODUCTION: Antiphospholipid antibodies (APA) clinical relevance in COVID-19 is controversial. We aimed to investigate the prevalence and prognostic value of conventional and non-conventional APA in COVID-19 patients. METHODS: This study was a multi-centric, prospective observational French cohort of patients hospitalized for COVID-19 suspicion. RESULTS: 249 patients were hospitalized for suspected COVID-19, including 154 with confirmed COVID-19 and 95 not confirmed. We found a significant increase in lupus anticoagulant (LA) positivity among COVID-19 positive patients (60.9% versus 23.7% in non-COVID19 patients, p

Background Coronavirus disease 2019 (COVID‐19) is a respiratory disease associated with vascular inflammation and endothelial injury. Objectives To correlate circulating angiogenic markers vascular endothelial growth factor A (VEGF‐A), placental growth factor (PlGF), and fibroblast growth factor 2 (FGF‐2) to in‐hospital mortality in COVID‐19 adult patients. Methods Consecutive ambulatory and hospitalized patients with COVID‐19 infection were enrolled. VEGF‐A, PlGF, and FGF‐2 were measured in each patient ≤48 h following admission. Results The study enrolled 237 patients with suspected COVID‐19: 208 patients had a positive diagnostic for COVID‐19, of whom 23 were mild outpatients and 185 patients hospitalized after admission. Levels of VEGF‐A, PlGF, and FGF‐2 significantly increase with the severity of the disease (P

Predictive dynamic simulations of virtual machining rely on accurate representation of eigenmodes and damping factors. Historically, the modeling of flexible workpieces requires experimental updating of general modal properties, especially due to a simplified definition of fixtures. In the present work a substructuring-based approach for a virtual machining simulation is developed. It is demonstrated on a vibration-prone boring of a thin-walled automotive workpiece. Fixture-affected zones are modeled via MacNeal-type approach. This enables for addressing the influence of clamping in the mechanical modeling of dynamics, and for creating specific models of typical fixture configuration. During simulation vibrations occur on similar frequencies to those observed on real machining. Resulting surface defects follow alike patterns in simulation and experiment.

International audience; Introduction Lupus Anticoagulant testing using dilute Russell Viper Venom Time (dRVVT) is challenging in patients receiving Direct Oral AntiCoagulants (DOAC) due to potential false positive results. In a multicenter study, we evaluated the in vitro removal of DOAC by activated charcoal (DOAC remove®), allowing reliable dRVVT testing. Materials and methods Patient samples were analyzed before and after treatment with DOAC remove® 49 apixaban, 48 rivaroxaban, 24 dabigatran and 30 none. DOAC plasma concentrations were measured using anti-Xa or diluted thrombin time assays. In a subset of 28 samples, DOAC concentrations were also measured using HPLC-MS/MS following treatment with DOAC remove®. DRVVT was performed using STA-Staclot dRVVT Screen®/Confirm® (Stago) or LAC-Screening®/Confirmation® (Siemens). Results Baseline median [min-max] concentrations were 94 [

Introduction Clinical benefit-risk balance of direct oral anticoagulants (DOAC) in atherothrombosis prevention differs between anti-Xa and anti-IIa drugs and their specific effect on platelet functions remains controversial. We hence investigated rivaroxaban and dabigatran effect on platelets in identical experimental conditions. Materials and methods Blood of fifteen healthy volunteers was spiked with DOAC which plasma concentrations were measured by specific anti-Xa or anti-IIa assays. Light transmission aggregometry measured in platelet-rich plasma used low doses of agonists: 0.5 mM arachidonic acid, 2.5 μM ADP, 0.5 μM epinephrine, 0.8 μg/ml collagen, 7.5 μM TRAP-6 and 0.5 pM tissue factor in the presence of H-Gly-Pro-Arg-Pro-OH to prevent fibrin polymerization. Platelet adhesion on collagen fibres was evaluated in whole blood under flow. Same experiments were reproduced in the presence of aspirin. Results Median [95% CI] plasma concentrations were of 28 [23–36], 128 [119–144] and 321 [293–361] ng/ml for rivaroxaban and 39 [34–45], 171 [166–193] and 353 [349–382] ng/ml for dabigatran. DOAC did not modify platelet aggregation or adhesion on collagen fibres at any tested concentrations. However, they delayed platelet aggregation secondary to coagulation activation with a more potent effect with dabigatran (p Conclusion Efficacy of combining DOAC and aspirin in atherothrombosis prevention would not stem from a direct antiplatelet effect of the formers but to their additive inhibitory effect on platelet aggregation secondary to coagulation activation. This effect differs according to DOAC molecules and may also result from the pleiotropic roles of the different coagulation factors targeted by DOAC.

The circulating metabolome provides a snapshot of the physiological state of the organism responding to pathogenic challenges. Here we report alterations in the plasma metabolome reflecting the clinical presentation of COVID-19 patients with mild (ambulatory) diseases, moderate disease (radiologically confirmed pneumonitis, hospitalization and oxygen therapy), and critical disease (in intensive care). This analysis revealed major disease- and stage-associated shifts in the metabolome, meaning that at least 77 metabolites including amino acids, lipids, polyamines and sugars, as well as their derivatives, were altered in critical COVID-19 patient’s plasma as compared to mild COVID-19 patients. Among a uniformly moderate cohort of patients who received tocilizumab, only 10 metabolites were different among individuals with a favorable evolution as compared to those who required transfer into the intensive care unit. The elevation of one single metabolite, anthranilic acid, had a poor prognostic value, correlating with the maintenance of high interleukin-10 and -18 levels. Given that products of the kynurenine pathway including anthranilic acid have immunosuppressive properties, we speculate on the therapeutic utility to inhibit the rate-limiting enzymes of this pathway including indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase.

Background Coronavirus disease 2019 (COVID-19) is a respiratory disease associated with endotheliitis and microthrombosis. Objectives To correlate endothelial dysfunction to in-hospital mortality in a bi-centric cohort of COVID-19 adult patients. Methods Consecutive ambulatory and hospitalized patients with laboratory-confirmed COVID-19 were enrolled. A panel of endothelial biomarkers and von Willebrand factor (VWF) multimers were measured in each patient ≤ 48 h following admission. Results Study enrolled 208 COVID-19 patients of whom 23 were mild outpatients and 189 patients hospitalized after admission. Most of endothelial biomarkers tested were found increased in the 89 critical patients transferred to intensive care unit. However, only von Willebrand factor antigen (VWF:Ag) scaled according to clinical severity, with levels significantly higher in critical patients (median 507%, IQR 428–596) compared to non-critical patients (288%, 230–350, p

International audience

Background Heparin-induced thrombocytopenia (HIT) is a rare complication of heparin treatments, and only a few large patient cohorts have been reported. In this study, biological and clinical data from 144 French patients with HIT were analyzed in comparison with the literature. Methods The diagnosis of HIT was confirmed in all patients by an immunoassay combined with serotonin release assay. In the literature, only cohorts of at least 20 HIT patients published from 1992 were selected for a comparative analysis. Results Two-thirds of patients were hospitalized in surgery and most were treated with unfractionated heparin (83.2% vs. 16.8% with low molecular weight heparin only). Thrombotic events in 54 patients (39.7%) were mainly venous (41/54). However, arterial thrombosis was more frequent after cardiac surgery (13.2% vs. 2.4% in other surgeries, p = 0.042) with a shorter recovery time (median = 3 vs. 5 days, p Conclusion This study shows that the mortality rate due to HIT has recently decreased in France, possibly due to earlier diagnosis and improved medical care. It also confirms the strong association between polymorphism FcγRIIA H131R and thrombosis in HIT.

Background The vast majority of COVID-19 patients experience a mild disease. However, a minority suffers from critical disease with substantial morbidity and mortality. Objectives To identify individuals at risk of critical COVID-19, the relevance of a seroreactivity against seasonal human coronaviruses was analyzed. Methods We conducted a multi-center non-interventional study comprising 296 patients with confirmed SARS-CoV-2 infections from four tertiary care referral centers in Germany and France. The ICU group comprised more males, whereas the outpatient group contained a higher percentage of females. For each patient, the serum or plasma sample obtained closest after symptom onset was examined by immunoblot regarding IgG antibodies against the nucleocapsid protein (NP) of HCoV 229E, NL63, OC43 and HKU1. Results Median age was 60 years (range 18-96). Patients with critical disease (n=106) had significantly lower levels of anti-HCoV OC43 nucleocapsid protein (NP)-specific antibodies compared to other COVID-19 inpatients (p=0.007). In multivariate analysis (adjusted for age, sex and BMI), OC43 negative inpatients had an increased risk of critical disease (adjusted odds ratio (AOR) 2.68 [95% CI 1.09 - 7.05]), higher than the risk by increased age or BMI, and lower than the risk by male sex. A risk stratification based on sex and OC43 serostatus was derived from this analysis. Conclusions Our results suggest that prior infections with seasonal human coronaviruses can protect against a severe course of COVID-19. Therefore, anti-OC43 antibodies should be measured for COVID-19 inpatients and considered as part of the risk assessment for each patient. Hence, we expect individuals tested negative for anti-OC43 antibodies to particularly benefit from vaccination against SARS-CoV-2, especially with other risk factors prevailing.

INTRODUCTION Direct oral factor Xa inhibitors (xabans) induce false positive results for lupus anticoagulant (LA) diagnosis. Consequently, it is suggested not to perform LA testing in xabans patients although it may be useful in selected patients. In this monocentric study, we evaluated xabans impact at trough levels (ie, just before the next intake) on LA diagnosis in treated patients using dilute Russell viper venom time (dRVVT) and two LA sensitive activated partial thromboplastin time (aPTT). METHODS Sixty patients receiving rivaroxaban (30) or apixaban (30) were included. Plasma concentrations were measured using specific anti-Xa assays. LA testing was performed using one dRVVT (LAC-Screening® /Confirm® ; Siemens) and two LA sensitive aPTT-based assays (Hemosil® Silica Clotting Time (SCT) Screen/Confirm; Werfen and Dade® Actin® Factor Sensitivity FSL/FS (Actin F); Siemens). RESULTS Median [min-max] concentrations were 23 [

International audience; Eftrenonacog-alfa is a recombinant factor IX-Fc fusion protein increasingly prescribed in hemophilia B patients. We aimed to assess its pharmacodynamics (PD) in real-life setting via FIX activity measurement and thrombin generation assay (TGA). Sixty samples from 15 severe hemophilia B treated patients were collected at different time points. FIX activity was measured using product-specific one-stage clotting assay (reference method) and two chromogenic assays (CSA) (Biophen FIX and Rox FIX). TGA was triggered with 1 pM tissue factor. Five parameters were analyzed: lag time (LT), time to peak (TTP), peak height (PH), endogenous thrombin potential (ETP), and velocity. PD models were built to characterize their relationships with FIX activity, using mixed effects models. Mean trough FIX level was estimated at 4.64 (±1.50) IU/dl with a recovery at 0.78 (±0.16) IU/dl per 1 IU/kg injected dose. FIX activity ranged between 1 and 86 IU/dl with 21.5 IU/dl median value. Biophen FIX and Rox FIX allowed reliable measurements except in samples with FIX 30%). PD models revealed that velocity was the most sensitive TGA parameter to FIX activity followed by PH, ETP, TTP and finally LT. Following FIX activity peak after eftrenonacog-alfa injection, velocity decreased first, followed by PH then ETP. Both CSA failed to accurately measure FIX in severe hemophilia B patients receiving eftrenonacog-alfa throughout the measuring range. TGA could be an additional valuable tool to evaluate hemostasis balance in treated patients.

Background Calibrated Automated Thrombography (CAT) has been widely used to assess in vitro thrombin generation as an informative intermediary phenotype of coagulation. Interlaboratory exercises have documented a worrisome poor reproducibility. There are some data on the normalisation with an appropriate external reference plasma (RP). This multicentre study of the French-speaking CAT Club aimed at providing further evidence for the usefulness of such a normalisation. Materials and Methods Lyophilised aliquots of a RP along with 3 plasmas (P1 = normal; P2 = hypo-; P3 = hypercoagulable) were sent to 34 laboratories (corresponding to 38 instruments). CAT was studied using 1 and 5 pM tissue factor and other dedicated reagents. Normalisation with the local RP in use in the laboratory could also be performed. Interlaboratory CVs were calculated for each plasma before and after normalisation. Results Regarding endogenous thrombin potential, a good discrimination between the 3 plasmas was achieved in all laboratories but there was no overlap after normalisation only. CVs were generally not reduced with the use of local RP but were generally improved with normalisation using the external RP, often becoming lower than 10%. Regarding P2 however, the benefit of normalisation was poor, and there were analytical difficulties as well, some laboratories being unable to get a useable signal. Conclusions We confirm that normalisation of CAT results with a suitable external RP is useful in “real life” practice as it often permits an acceptable level of interlaboratory variability. In case of frank hypocoagulability, further improvements are required to get reliable, potentially clinically relevant results.

Summary Bleeding risk is not predictable in patients with factor XI (FXI; F11) deficiency. In this prospective study, our objectives were to determine the biological determinants for bleeding risk in patients with heterozygous FXI deficiency. Patients were classified as either bleeding patients or non-bleeding patients by calculating the bleeding score (BS) described for von Willebrand disease. Primary haemostasis, thrombin generation, thromboelastometry, procoagulant proteins, inhibitors, fibrinolysis, and F11 gene mutations were compared between bleeding and non-bleeding patients. Thirty-nine patients were included. BS significantly correlated with clinical assessment (P = 0·001), and a score over 3 discriminated between bleeding (n = 15) and non-bleeding (n = 24) patients (P = 0·034). Despite normal values, von Willebrand factor (VWF) and thrombomodulin (TM) plasma levels were significantly lower in bleeding patients than non-bleeding patients [ristocetin cofactor activity (VWF:RCo) = 80·6 ± 29·7 iu/dl and 101·8 ± 29·5 iu/dl respectively, P = 0·043; and VWF antigen (VWF:Ag) = 84·0 ± 28·0 iu/dl and 106·3 ± 36·1 iu/dl respectively, P = 0·035; and TM = 17·7 ± 11·7 ng/ml and 23·6 ± 9·7 ng/ml respectively, P = 0·043]. When considering BS as a continuous variable, only VWF:RCo remained significant (P = 0·042), which accounted for 11% of the variability in BS.

Microparticles (MPs) are membrane fragments ranging in size from 0.1 to 1 microm, and are considered as biomarkers reflecting prothrombotic state in many clinical diseases. The clinical course of myeloproliferative neoplasms (MPN) being frequently complicated by thrombotic events, we determined the MPs activity, i.e. circulating procoagulant activity (CPA), in polycythemia vera (PV) and essential thrombocythemia (ET) patients. To evaluate the influence of MPs on the coagulation, a thrombin generation test was realized in the absence and presence of thrombomodulin (TM). Compared with controls, patients had a higher CPA (24.0+/-9.0 vs 10.6+/-4.4 nM, p

Thin tubular parts are often subject to turning process during manufacturing. The increasing compliance of the workpiece, which is associated to tool displacement and to matter removal, can give rise to chatter, leading to poor surface quality or premature machine/tool damage. The present work addresses an experimental case of turning a steel thin-walled tube featuring intense vibrations with variable parameters. Observations of transient records during the pass suggest a strong influence of the matter removal on the eigenfrequencies of the system, while the tool's motion implies strong variation of the modal projection of the cutting force. Another characteristic phenomenon is the intermittency of the vibrations and discontinuous chatter frequency evolution. These phenomena are reproduced and analyzed numerically. By means of a finite element modeling, the part's geometry variation during the pass is taken into account. Finally, a stability analysis is carried out for several states of this evolutive system in order to gather insight into the steady cutting conditions.

International audience; Bleeding risk is not predictable in patients with factor XI (FXI; F11) deficiency. In this prospective study, our objectives were to determine the biological determinants for bleeding risk in patients with heterozygous FXI deficiency. Patients were classified as either bleeding patients or non-bleeding patients by calculating the bleeding score (BS) described for von Willebrand disease. Primary haemostasis, thrombin generation, thromboelastometry, procoagulant proteins, inhibitors, fibrinolysis, and F11 gene mutations were compared between bleeding and non-bleeding patients. Thirty-nine patients were included. BS significantly correlated with clinical assessment (P=0*001), and a score over 3 discriminated between bleeding (n=15) and non-bleeding (n=24) patients (P=0*034). Despite normal values, von Willebrand factor (VWF) and thrombomodulin (TM) plasma levels were significantly lower in bleeding patients than non-bleeding patients [ristocetin cofactor activity (VWF:RCo)=80*6±29*7 iu/dl and 101*8±29*5iu/dl respectively, P=0*043; and VWF antigen (VWF:Ag)=84*0±28*0 iu/dl and 106*3±36*1 iu/dl respectively, P=0*035; and TM=17*7±11*7ng/ml and 23*6±9*7ng/ml respectively, P=0*043]. When considering BS as a continuous variable, only VWF:RCo remained significant (P=0*042), which accounted for 11% of the variability in BS.

International audience; Compared with 537 parous controls with no history of pregnancy loss, a lower thrombomodulin-related inhibition of the endogenous thrombin potential was measured in 264 cases with previous unexplained pregnancy loss, especially when losses occurred between 9 and 12 weeks of gestation. Adjusting age, protein S, factor VIII, factor V Leiden, and prothrombin G20210A did not change the results.

SummaryThe thrombin generation test is used to study coagulation in patients with haemorrhagic diseases or with high thrombotic risk. To our knowledge, this is the first study investigating the relative influence of coagulation factors on thrombin generation in plasma. The aim was to investigate the influence of coagulant factors, anticoagulant factors, and tissue factor (TF) on three parameters: endogenous thrombin potential (ETP), peak thrombin concentration, and lag time for the appearance of thrombin. At a low TF concentration, all factors except factor XI influenced thrombin generation. At a high TF concentration, only the factors of the extrinsic pathway exerted an influence. ETP and peak thrombin were linearly correlated to factor II concentration. Factor V and factor VII effects increased hyperbolically with factor concentration. The influence of factor X on thrombin generation depended onTF concentration. In the absence of factorVIII and factor IX, ETP fell to 60–70% of the normal when peak thrombin fell to 25–30% of the normal. Fibrinogen concentration influenced ETP and peak thrombin and decreasing fibrinogen levels shortened the lag time. As expected, decreasing antithrombin concentration caused dramatic increases in thrombin generation. Protein S prolonged the lag time, especially at a low TF concentration. No effect of protein C was observed, likely due to the absence of thrombomodulin. The thrombin generation test was more sensitive to factor deficiencies at low than at high TF concentration. ETP was not the most critical parameter for studying coagulation factor deficiencies. Instead, peak thrombin was the most sensitive parameter.

International audience; BACKGROUND: The vitamin K epoxide reductase complex subunit 1 (VKORC1) recycles endogenous vitamin K, a cofactor for vitamin K-dependent coagulation factor synthesis. Common polymorphisms in VKORC1, the gene coding for VKORC1, have been found to affect the dose response to vitamin K antagonists, and to confer an increased risk of vascular diseases in a Chinese population. The aim of this study was to evaluate the association between the VKORC1 1173C > T polymorphism and venous thromboembolism (VTE). METHODS: We report the results of a case-control study designed to evaluate interactions between acquired and inherited risk factors of VTE. We studied 439 cases hospitalized with a first venous thromboembolic event that was not related to a major acquired risk factor for VTE, and 439 matched controls. The VKORC1 1173C > T polymorphism was selected for genotyping as the tagging single-nucleotide polymorphism for previously identified VKORC1 haplotypes. RESULTS: The relationship between VTE and the VKORCI 1173C > T polymorphism was consistent with a recessive model. The frequency of the VKORCI TT genotype was lower in cases than in controls. The odds ratio (OR) (95% CI) was 0.62 (0.41-0.94) for the TT genotype as compared to CT/CC genotypes. Adjustment on cardiovascular diseases, body mass index, factor V (FV) and prothrombin gene mutations did not alter the results. CONCLUSIONS: In this case-control study, the frequency of the VKORCI TT genotype was lower in patients with VTE than in matched controls. The clinical consequence of these results remains to be determined, but gives new perspectives for exploration of the role of VKORCI polymorphism in the pathogenesis of VTE.

International audience; In the HIV infection, the short time-scale between the HIV-induced cardiovascular events and the onset of antiretroviral therapy elicits a thrombophilic co-factor that worsens the induced atherosclerosis. We compared the factor VIII plasma activity, previously implicated in arterial and venous thrombosis, with a surrogate marker of atherosclerosis, the carotid intima-media thickness, and with the usual atherosclerosis risk factors in 154 HIV infected outpatients. The FVIII plasma activity is significantly associated with the carotid intima-media thickness and, strongly, with blood glucose and triglycerides levels. A raised FVIII plasma activity is an important feature of the metabolic syndrome and a putative co-factor of HAART induced cardiovascular events. Thus the prevention of the HAART-induced cardio-vascular events should probably not be exclusively focused on atherosclerosis but likewise on the thrombus formation process.

We report on a 69-year-old woman with B-lineage acute lymphoblastic leukemia. Cytogenetic studies at diagnosis with R banding showed an insertion, ins(4;11)(q21;q13q23). Fluorescence in situ hybridization (FISH) with whole chromosome painting probes confirmed the insertion of chromosome 11 material into chromosome 4. FISH using the MLL probe showed the translocation of the 5' end of MLL into chromosome 4. Since the 5'MLL-3'AF4 fusion transcript was detected by a reverse transcriptase polymerase chain reaction, we concluded that the insertion of part of chromosome 11 split the AF4 gene in two, resulting in the presence of the 5'MLL-3'AF4 fusion gene on the der(4) instead of the der(11), as commonly observed. Our findings stress the value of combining banding cytogenetics with FISH and molecular techniques to better assess rearrangements in leukemia.

Fatal cerebral hemorrhage involving the left thalamus in a neonate was attributed to deep cerebral vein thrombosis. Although antithrombin levels were at the lower end of the normal range, family and genetic studies showed constitutional type I antithrombin deficiency related to a novel missense mutation in the antithrombin gene.

A Ser 460 to Pro mutation of protein S (PS), involving a T to C transition in exon XIII of the protein S alpha (PROS1) gene and known as the Heerlen polymorphism, was found in 16 of 85 symptomatic patients with PS deficiency (18.8%) and only 1 of 113 healthy subjects (0.8%). Another frequent polymorphism was described in exon XV of the PROS1 gene, in the codon for Pro 626 (CCA/CCG). We found that Heerlen polymorphism was associated with allele CCA and not with allele CCG, suggesting a probable transmission by a common ancestor. Most subjects bearing the Ser 460 to Pro mutation were deficient in free PS, but had normal total PS levels. Normal levels of the C4b-binding protein (C4b- BP) isoform containing a beta chain (C4b-BP beta +) ruled out increased C4b-BP beta + as a cause of the free-PS deficiency. The binding curves of the mutated (Heerlen) PS on C4b-BP immobilized on microplates were biphasic, suggesting that one molecule of C4b-BP can bind two molecules of Heerlen PS. Because normal PS binds to C4b-BP with 1:1 stoichiometry, this may explain the free-PS deficiency observed in patients carrying the Ser 460 to Pro mutation.

SummaryThe protein C Gla domain was studied in six families presenting a type II hereditary deficiency characterized by low activity in a coagulation assay and normal activity in an amidolytic assay. Five of these mutations, previously described by our group, affected Arg-5, Arg-1, Arg 229 and Ser 252. We report here the first natural Glu 7 to Asp mutation in a sixth family.We evaluated the binding of the mutated protein C to Hn, a monoclonal antibody (mAb) known to recognize the sequence Phe 4 to Arg 9 of the Gla domain; the presence of calcium ions suppresses the recognition of this epitope by Hn. Mutation of Arg 229 to Gin and Ser 252 to Asn did not modify the inhibition of protein C binding, whereas the Arg-1 to His mutation resulted in a loss of inhibition in the presence of CaCl2. This suggests that the protein C of this patient shows impaired carboxylation.The protein C from patients bearing the mutations Arg-5 to Trp, Arg-1 to Cys and Glu 7 to Asp bound poorly to Hn mAb, even in the absence of calcium ions. The calcium affinity of the Gla domain was studied by pseudo-affinity chromatography, in which protein C was successively eluted from a Mono Q column by CaCl210 mM and NaCl 0.6 M. Protein C from the patient bearing the Arg-5 to Asp mutation had a normal elution profile, suggesting that a modification of the propeptide cleavage site impairs the conformation of the Gla domain but not carboxylation. Conversely, the patient bearing the mutation Arg-1 to Cys had an abnormal elution profile, showing that calcium binding affinity was impaired probably due to a defective carboxylation (the behaviour of the Glu 7 to Asp mutant lacking one Gla residue validated our experimental approach).These results confirm that mutations in the serine protease domain do not modify the conformation of the N-terminal part of the Gla domain. Arg-1 to His, Arg-1 to Cys and Glu 7 to Asp mutations strongly modified affinity for calcium ions, whereas the Arg-5 to Trp mutation probably modifies the conformation of the Gla domain.

SummaryActivated protein C reduces thrombin generation by inactivating factors V and VIII in the presence of protein S. This prompted us to develop an assay which would allow specific exploration of this reaction. The total amount of thrombin formed in plasma after activation by tissue factor and phospholipids was reduced by adding thrombomodulin. This addition allowed protein C to be activated by endogenous thrombin. The inhibition of thrombin generation (ITG) due to protein C activation could be measured by comparing thrombin formation in the presence and in the absence of thrombomodulin. ITG increased with both protein C and protein S concentrations. Normal values of ITG expressed as a percentage were between 40 and 65% and were not influenced by age or sex. ITG increased in patients under heparin therapy, decreased in patients under oral anticoagulant therapy and was decreased in women using oral contraceptives. This method could be used for screening patients for protein C and protein S deficiencies.