Large Cohort Study of Central Venous Catheter Thrombosis during Intravenous Antibiotic Therapy.

The frequency and risk factors for central venous catheter-related thrombosis (CRT) during prolonged intravenous (i.v.) antibiotic therapy have rarely been reported. The primary objective of this study was to evaluate the frequency, incidence, and risk factors for CRT among patients being treated with prolonged i.v. antibiotic therapy. The secondary objective was to describe the clinical manifestations, diagnostic evaluation, and clinical management. This cohort study was conducted between August 2004 and May 2010 in a French referral center for osteoarticular infections. All patients treated for bone and joint infections with i.v. antimicrobial therapy through a central venous catheter (CVC) for ≥2 weeks were included. Risk factors were identified using nonparametric tests and logistic regression. A case-control study investigated the role of vancomycin and catheter malposition. A total of 892 patients matched the inclusion criteria. CRT developed in 16 infections occurring in 16 patients (incidence, 0.39/1,000 catheter days). The median time to a CRT was 29 days (range, 12 to 48 days). Local clinical signs, fever, and secondary complications of CRT were present in 15, 8, and 4 patients, respectively. The median C-reactive protein level was 95 mg/liter. The treatment combined catheter removal and a median of 3 months (1.5 to 6 months) of anticoagulation therapy. The outcome was good in all patients, with no recurrence of CRT. Three risk factors were identified by multivariate analysis: male sex (odds ratio [OR], 5.4; 95% confidence interval [CI], 1.1 to 26.6), catheter malposition (OR, 5.3; 95% CI, 1.6 to 17.9), and use of vancomycin (OR, 22.9; 95% CI, 2.8 to 188). Catheter-related thrombosis is a rare but severe complication in patients treated with prolonged antimicrobial therapy. Vancomycin use was the most important risk factor identified.

Functional Flow Cytometric Assay for Reliable and Convenient Heparin-Induced Thrombocytopenia Diagnosis in Daily Practice.

Reliable laboratory diagnosis of heparin-induced thrombocytopenia (HIT) remains a major clinical concern. Immunoassays are highly sensitive, while confirmatory functional tests (based on heparin-dependent platelet activation) lack standardization. We evaluated the diagnostic performance of a functional flow cytometric assay (FCA) based on the detection of heparin-dependent platelet activation with an anti-p-selectin. A total of 288 patients were included (131 HIT-positive and 157 HIT-negative) with a HIT diagnosis established by expert opinion adjudication (EOA) considering clinical data and local laboratory results. The FCA was centrally performed in a single laboratory on platelet-rich plasma, using a very simple four-color fluorometer. The results were standardized according to the Heparin Platelet Activation (HEPLA) index. The serotonin release assay (SRA) was performed in the four French reference laboratories. Based on the final HIT diagnosis established by EOA, the sensitivity and specificity of the FCA were 88 and 95%, respectively, values very similar to those of the SRA (88 and 97%, respectively). This study showed that the FCA, based on easily implementable technology, may be routinely used as a reliable confirmatory test for HIT diagnosis.

Heparin-induced thrombocytopenia: Construction of a pretest diagnostic score derived from the analysis of a prospective multinational database, with internal validation.

BACKGROUND: Diagnosis of heparin-induced thrombocytopenia (HIT) requires pretest probability assessment and dedicated laboratory assays. OBJECTIVE: To develop a pretest score for HIT. DESIGN: Observational; analysis of prospectively collected data of hospitalized patients suspected with HIT (ClinicalTrials.gov NCT00748839). SETTING: Thirty-one tertiary hospitals in France, Switzerland, and Belgium. PATIENTS: Patients tested for HIT antibodies (2280 evaluable), randomly allocated to derivation and validation cohorts. MEASUREMENTS: Independent adjudicators diagnosed HIT based on the prospectively collected data and serotonin release assay results. RESULTS: Heparin-induced thrombocytopenia was diagnosed in 234 (14.7%) and 99 (14.5%) patients in the two cohorts. Eight features were associated with HIT (in brackets, points assigned for score calculation of the score): unfractionated heparin (1); therapeutic-dose heparin (1); cardiopulmonary bypass (cardiac surgery) (2); major trauma (3); 5- to 21-day interval from anticoagulation initiation to suspicion of HIT (4); ≥40% decrease in platelet count over ≤6 days (3); thrombotic event, arterial (3) or venous (3). The C-statistic was 0.79 (95% CI, 0.76-0.82). In the validation cohort, the area under the receiver operating characteristic curve was 0.77 (95% CI, 0.74-0.80). Three groups of scores were defined; HIT prevalence reached almost 30% in the high-probability group. LIMITATION: The performance of the score may depend on settings and practices. CONCLUSION: The objective, easy-to-collect, clinical features of HIT we evidenced were incorporated into a pretest score, which may guide clinical decisions regarding diagnostic testing and anticoagulation.

Antithrombin alfa in hereditary antithrombin deficient patients: A phase 3 study of prophylactic intravenous administration in high risk situations.

During surgery and childbirth, patients with hereditary antithrombin (AT) deficiency are at high risk for thrombosis, and heparin prophylaxis may not be sufficiently efficacious. In these patients, exogenous AT may be used in association with heparin. A recombinant human AT (generic name: antithrombin alfa) has been developed. This multi-center study assessed the efficacy and safety of prophylactic intravenous administration of antithrombin alfa to hereditary AT deficient patients in high risk situations, including elective surgery, childbirth, or cesarean section. Antithrombin alfa was administered prior to and during the high risk period for restoration and maintenance of AT activity at 100% of normal. Heparin, low-molecular-weight heparin, and/or vitamin K antagonists were used according to standard of care. The primary efficacy endpoint was the incidence of acute deep vein thrombosis (DVT) from baseline up to day 30 post dosing as assessed by independent central review of duplex ultrasonograms and/or venograms. Safety was assessed based on adverse events (AEs) and laboratory evaluations. Five surgical and nine obstetrical hereditary AT deficiency patients received antithrombin alfa for a mean period of seven days. No clinically overt DVT occurred. Central review of ultrasonograms identified signs of acute DVT in two out of 13 evaluable patients. No antithrombin alfa-related AEs were reported. No patient developed anti-antithrombin alfa antibodies. In conclusion, this study suggests that antithrombin alfa is a safe and effective alternative to human plasma-derived AT for treating hereditary AT deficiency patients at high risk for thromboembolic events.

Afibrinogenemia resulting from homozygous nonsense mutation in A alpha chain gene associated with multiple thrombotic episodes.

Congenital afibrinogenemia is a rare disorder characterized by the absence in circulating fibrinogen, a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta and gamma). Although predisposition to thrombosis is a well known feature of dysfibrinogenemia, the relatively frequent thrombotic manifestations seen in congenital afibrinogenemia are puzzling. We herein report a mutational analysis of a young afibrinogenemic man from Turkey with multiple thrombo-embolic events involving both arteries and veins. Purified DNAs of the propositus was used for amplification by polymerase chain reaction of all the exons of the A subunit gene with primers allowing the analysis of the intron-exon boundaries. Analysis of the genes coding for the three fibrinogen chains of the propositus found a homozygous G to A transition in the exon 5 of the A alpha chain gene (g.g4277a; access number gi458553). The TGG to TGA codon change predicts a homozygous W315X in the A alpha chain (p.W334X when referring to the translation initiation codon). Both parents and his brother were found to carry this heterozygous mutation. This is the first report of a patient homozygous for this rare mutation associated with afibrinogenemia. Our patient was free of known risk factors as well as diseases associated with thrombosis including atherosclerosis, vasculitis, Buerger's disease, and it seems therefore probable that afibrinogenemia itself might have contributed to both arterial and venous thrombosis.

Type of Combined Contraceptives, Factor V Leiden Mutation and Risk of Venous Thromboembolism.

OBJECTIVE: This article estimates the interaction between types of combined hormonal contraception (CHC) and factor V Leiden (FVL) mutation on the risk of venous thrombosis event (VTE). SUBJECTS AND METHODS: All premenopausal women with first incident VTE who were referred to our unit (Paris, France) between 2000 and 2009 were included in this case-only study. Differences in interactions by progestin type were assessed on a multiplicative scale, assuming the independence of genotype and prescription of type of CHC. RESULTS: Among 2,613 women with VTE, 15.9% had a FVL and 69% used CHC. The interaction between CHC use and presence of FVL on VTE risk was statistically significant (1.37, 1.06-1.77 95% confidence interval [CI]). This interaction appeared higher for drospirenone 1.99 (1.18-3.38 95% CI) (n = 98) or cyproterone acetate users 1.71 (1.20-2.45 95% CI) (n = 326), but not significant for 1st or 2nd or norgestimate CHC users. The results were similar when excluding women with a family history of VTE or with provoked VTE. In this sub-group of women, these interactions appeared higher for third generation, cyproterone acetate and drospirenone CHC users as compared with 1st or 2nd or norgestimate CHC users (odds ratio [OR], 1.68 [1.04-2.70; 95% CI], 2.91 [1.71-4.95 95% CI], 3.22 [1.54-6.73 95% CI], respectively). CONCLUSION: Our results show that the interaction between FVL and CHC use differ by progestin type, which is higher in CHC containing third-generation progestin, drospirenone or cyproterone acetate, compared with second generation. Further studies are needed to assess the cost-effectiveness of biological thrombophilia screening (FVL) when such prescription of CHC is planned.

Severe prekallikrein deficiencies due to homozygous C529Y mutations.

Two consecutive severe prekallikrein deficiencies were investigated. The first was identified in a 63-year-old patient admitted for ischemic stroke. The second deficiency was identified in a 38-year-old patient admitted for a second-trimester pregnancy loss. A homozygous C529Y mutation was identified for both cases, whereas they are unrelated and no consanguineous marriage is known from the patients. These data point to a possible high frequency of this mutation as a cause of prekallikrein deficiency.

First venous thromboembolism and hormonal contraceptives in young French women.

Information on the clinical and biological characteristics of combined hormonal contraceptives (CHC) users experiencing a venous thromboembolism (VTE) event is scarce. Better knowledge of factors determining the VTE risk in CHC users could help identify women at high risk.Data were obtained from a large cohort of consecutive women with the first documented VTE event. Cross-sectional analysis of clinical and biological characteristics of the women was performed.Of the 3009 women with the first VTE included, 31% were nonusers and 69% CHC users at time of VTE. CHC users were significantly younger (29.0 ±â€Š7.2) than nonusers (31.6 ±â€Š7.1) (P < .001). No difference in VTE familial history was observed between the 2 groups. Compared with nonusers, the CHC users experienced more frequently pulmonary embolism: odds ratio (OR) = 1.28 (1.06-1.55; 95% confidence interval [CI]), factor V Leiden mutations were more frequent in this group (OR = 1.41 [1.11-1.80; 95% CI]). Venous sclerotherapy and travel were associated with VTE in CHC users, whereas surgery and bed rest were significantly associated with VTE in nonusers. Finally, 2/3 of CHC users with VTE had additional VTE risk factors.CHC users experiencing the first VTE differ from nonusers with respect to clinical and genetic background. Better understanding of the characteristics of VTE and associated risk factors could allow more appropriate management of these women and contribute to more accurate benefit-risk assessment before prescribing a CHC.

Combined Hormonal Contraceptives and First Venous Thrombosis in Young French Women: Impact of Thrombotic Family History.

CONTEXT: In UK and French, but not World Health Organization (WHO), guidelines for combined hormonal contraception (CHC), family history of a venous thromboembolism (VTE) is a condition for which the theoretical risks usually outweigh the advantages of using CHC. OBJECTIVE: We estimated the prevalence of inappropriate prescriptions of CHC according to several international guidelines and their impact on VTE. DESIGN: A single-center observational study. SETTING: Hemostasis unit outpatient clinic (Paris, France). POPULATION: A total of 2088 French CHC users of childbearing age with a first documented VTE who were referred to our unit between 2000 and 2009. METHODS: Data were collected by a standardized questionnaire during a medical consultation. Family history of VTE was analyzed according to definitions from international recommendations (VTE before age 45 years, United Kingdom; before age 50 years, France). A CHC prescription was considered inappropriate for women with vascular contraindications and/or a family history of VTE. Cross-sectional analysis of the clinical and biological characteristics was performed. MAIN OUTCOME MEASURES: Prevalence of inappropriate prescription of CHC and potentially preventable events were estimated. RESULTS: According to the WHO, UK, or French guidelines, 8.8%, 18.9%, and 25.9%, respectively, of CHC prescriptions were considered inappropriate. Compliance with these guidelines could reduce the corresponding number of VTEs by 6.3%, 13.5%, and 18.5%, respectively. Characteristics of the women were similar. CONCLUSION: Our results suggest inappropriate CHC prescriptions are prevalent among CHC users with first VTE. The appropriate way to take family history of VTE into account should be further clarified.

Impact of a pneumatic tube system transport on hemostasis parameters measurement: the experiment of Cochin universitary hospital (AP-HP, Paris, France).

Samples transported by pneumatic tube system are submitted to forces of acceleration and deceleration which can affect laboratory parameters. At Cochin hospital, majority of samples of hemostasis, except for platelets tests, are transported by pneumatic tube system. The objective of this study was to evaluate the impact of a pneumatic tube system (PTS) transport compared to hand-delivered transport on samples and to qualify Cochin hospital PTS according to requirements of standard ISO 15189. A bibliographical study was made and showed that pneumatic tube system particularly influences platelets tests. Four citrate tubes were collected in 5 healthy volunteers in the maternity: 2 tubes were transported by PTS and 2 others were hand-delivered to the laboratory. Five coagulation tests were analyzed: prothrombine time (PT), activated partial thromboplastin time (aPTT), factor (F) V, FVIII and platelet closure time with PFA-100TM collagen/epinephrine. For each volunteer, the results obtained by PTS and by hand-delivered transport were compared with formula usually used for biological analysis retake: 2.8 x standard deviation of reproductibility variation coefficient (SH GTA 01, COFRAC). This study did not show an impact of PTS on PT, aPTT, FV and FVIII. For PFA-100TM collagen/epinephrine, we noted an impact on 2/5 volunteers. These results, in agreement with the literature, led to the conclusion that Cochin hospital PTS is in compliance to transport samples for usual coagulation tests except platelet tests. This study allowed to issue French recommendations for PTS transport of hemostasis tubes qualification available on "Groupe français d'hémostase et thrombose" Web site.

Thrombotic risk according to SERPINC1 genotype in a large cohort of subjects with antithrombin inherited deficiency.

Inherited quantitative (type I) or qualitative (type II) antithrombin deficiency (ATD) due to mutations in the SERPINC1 gene is a well-known risk factor for venous thromboembolism. ATD may also increase risk for arterial thrombosis. Few studies have investigated risk for thrombosis according to mutations. We addressed this topic in a large retrospective cohort study of 540 heterozygous carriers of SERPINC1 mutations and compared risk for first venous or arterial thrombosis associated with carrying of different type II or type I mutations. No clear difference in risk for first venous thrombotic event was observed among type I (missense or null), type IIRS or type IIPE mutation carriers except for a few variants that displayed lower risk [all events, adjusted relative risk: Cambridge II: 0.42 (95 %CI 0.25-0.70), Dublin: 0.35 (95 %CI 0.13-0.99)]. IIHBS mutation carrying was associated with a clearly lower risk than type I mutation carrying [0.28 (95 %CI 0.20-0.40)]. These differences in risk were observed for both all venous thrombotic events and pulmonary embolism associated with deep venous thrombosis. The HBS group was also heterogeneous, with AT Budapest 3 carriers displaying a non-significantly different risk [0.61 (95 %CI 0.31-1.20)] compared to type I mutation carriers. We also studied risk for arterial thrombosis and found no significant influence of mutation type. Altogether, our findings suggest a place for SERPINC1 genotyping in the diagnosis of ATD.

PROS1 genotype phenotype relationships in a large cohort of adults with suspicion of inherited quantitative protein S deficiency.

Inherited protein S deficiency (PSD) is an established risk factor for venous thromboembolism (VTE). However, data are conflicting concerning risk of VTE associated with decreased free PS level (FPS) and information on PROS1 genotype-phenotype relationship is sparse. In a retrospective cohort of 579 patients with inherited type I/III deficiency suspicion, PROS1 genotyping was performed and the effect of genotype on FPS and on VTE risk was investigated. We found 116 (including 65 novel) detrimental mutations (DM) in 222 (type I/III in 194, type II in 28), PS Heerlen in 74, possibly non DM in 38 and no mutation in 245 subjects. Among DMs, type I/IIIDMs only were found in subjects with FPS< 30 %. Prevalence of type I/III DM decreased with increasing FPS level. Risk of VT associated with FPS level and genotype was studied in the 467 subjects with personal or family history of thrombosis. Only type I/IIIDM carriers presented with an increased risk of VTE [1.41 (95 %CI (1.05-1.89)] compared to subjects with no mutation. Among the group of type I/IIIDM heterozygotes and subjects with no mutation, the optimal FPS cut-off point for identifying subjects at increased VTE risk was searched for. We found that only subjects with FPS< 30 % and type I/IIIDM presented with an increased risk [1.48 (95 %CI 1.08-2.04)]. Our findings confirm the value of a cut-off FPS level for identifying subjects at increased VTE risk far below the lower limit of the normal range and suggest a place for PROS1 genotyping in PSD diagnosis strategy.

PT, aPTT, TT and the hemostatic safety threshold of dabigatran and rivaroxaban.

The proposals of the Working group on perioperative hemostasis (Groupe d'intérêt en hémostase péri-opératoire (GIHP)) concerning the perioperative management of patients receiving the direct oral anticoagulants (DOACs) are based on the measure of their anticoagulant activities (anti-Xa for rivaroxaban and anti-IIa for dabigatran) with a safety threshold ≤ 30 ng/mL. If the dosage of the drug is not available, proposals are based on the combination of a PT ≥80% and an aPTT ≤1.20. The aim of our study was to evaluate the performance of PT, aPTT and thrombin time to predict values above or below the safety threshold. The measurement of DOACs concentration was carried out in 64 samples from patients treated with rivaroxaban and 48 samples from patients treated with dabigatran. The PT and aPTT were measured for all samples, while the TT was measured only for patients receiving dabigatran. The absence of agreement between the global hemostasis tests and the DOACs concentrations was observed for 10% of patients receiving dabigatran and 27% of patients with rivaroxaban treatment. Apart from dabigatran for which the predictive negative value of PT and aPTT or TT allows to exclude a concentration >30 ng/mL in 100% of cases, our results highlight the risk of misinterpretation when using global coagulation tests (PT and aPPT) for determination of the safety threshold for patients receiving the DOACs.

Peri-procedural management of dabigatran and rivaroxaban: Duration of anticoagulant discontinuation and drug concentrations.

BACKGROUND: Peri-procedural management of direct oral anticoagulants (DOAC) is challenging. The optimal duration of pre-procedural discontinuation that guarantees a minimal DOAC concentration ([DOAC]) at surgery is unknown. The usual 48-hour discontinuation might not be sufficient for all patients. OBJECTIVES: To test the hypothesis that a 48-hour DOAC discontinuation is not sufficient to ensure a minimal per-procedural [DOAC], defined as [DOAC]<30ng/mL. To investigate the factors associated with per-procedural [DOAC]. To evaluate the ability of normal PT and aPTT to predict [DOAC]<30ng/mL. METHODS: Patients treated with dabigatran or rivaroxaban, and requiring any invasive procedure were included in this multicentre, prospective, observational study. [DOAC], PT and aPTT were measured during invasive procedure. RESULTS: Sixty-five patients were enrolled. Duration of DOAC discontinuation ranged from 1-168h. Per-procedural [DOAC] ranged from <30 to 466ng/mL. [DOAC]<30ng/mL occurred more frequently after 48-hour discontinuation than after a shorter delay. [DOAC] remained ≥30ng/mL in 36% and 14% of measurements performed 24-48h and 48h-120h after discontinuation, respectively. According to ROC curve, a cut-off value of 120hours for DOAC discontinuation had a better specificity than a cut-off value of 48hours to predict [DOAC]<30ng/mL. Normal PT and aPTT ratios had good specificity and positive predictive value, but limited sensitivity (74%) and negative predictive value (73%) to predict [DOAC]<30ng/mL. CONCLUSIONS: A 48-hour discontinuation does not guarantee a [DOAC]<30ng/mL in all patients. Normal PT and aPTT are flawed to predict this threshold and could not replace specific assays. Further studies are needed to define the relationship between per-procedural [DOAC] and clinical outcomes.

[Non-VKA oral anticoagulants: an update for the clinical biologists]. / Anticoagulants directs oraux : actualités pour les biologistes.

Non-VKA oral anticoagulants (NOACs), thanks to their ease of use and their similar or superior safety/efficacy profiles versus warfarin, have now widely reached the lucrative market of anticoagulation. However, while the marketing authorization holders always claim, in a quite unclear way that no monitoring is required, accumulative evidence and cases of major bleeding have been described in the literature and reported by spontaneous reporting systems at the regulator's level. These compounds are usually given at fixed doses without routine coagulation monitoring. However, new data suggests that an assessment of the response at the individual level could improve the benefit-risk ratio of, at least dabigatran. Therefore, in certain patient populations, i.e. acute or chronic renal impairment or multiple drug interactions, measurement of drug exposure may be useful to ensure an optimal treatment response. More specific circumstances such as patients experiencing a haemorrhagic or thromboembolic event during the treatment duration, patients who require urgent surgery or an invasive procedure, or patient with a suspected overdose could benefit from such a measurement. This article aims at providing guidance on how to best estimate the intensity of anticoagulation using laboratory assays in daily practice.

Progestogen-only contraception in women at high risk of venous thromboembolism.

The objective of the study was to evaluate the venous impact of a progestogen-only contraception on women at high risk of venous thromboembolism (VTE). In this retrospective cohort study, 204 consecutive women at high risk of VTE were recruited between January 1992 and June 1997 and were prospectively followed. Women using chlormadinone acetate (CMA) at antigonadotropic doses (n=102) were matched by age and date of referral and history of venous thrombosis with women who had no hormonal contraception (n=102). During follow-up (mean of 33 months), nine episodes of VTE were observed: three in women receiving CMA and six in nontreated women. Using the Cox model to adjust for confounding variables such as age, thrombophilia and body mass index, the relative risk of VTE associated with the use of CMA was not significant [relative risk: 0.8 (0.2-3.9)]. These reassuring results need to be confirmed in other prospective studies.

[Pregnancy-associated venous thrombosis in women with hereditary heterozygous factor V Leiden and/or factor II gene mutations]. / Risque de thrombose lié à la grossesse chez les femmes porteuses d'une mutation hétérozygote du facteur V Leiden, du facteur II ou de leur association.

The risk of venous thromboembolism (VTE) in pregnant women with heterozygous factor V Leiden and/or heterozygous factor II 20210A gene mutations is poorly documented, and the need for prophylaxis is therefore controversial. We retrospectively studied 208 women with hereditary thrombophilia (heterozygous FV Leiden and/or factor II gene mutations), who had a total of 406 full-term pregnancies, including 10 with thromboprophylaxis. The ante- and post-partum incidence of VTE was significantly higher in women with both mutations (17.8 %) than in women with FII gene mutation alone (6.2%) p = 0.003. In contrast, there was no significant difference between women with FV+FII mutation and those with FV mutations alone (10%). Thus, the two most common hereditary risk factors for thrombophilia seem to have an additive rather than a synergistic effect on the antepartum/post-partum risk of VTE. In contrast, a previous history of VTE before pregnancy in women with both the FV and the FII gene mutations was associated with a very high risk of VTE (50%). The incidence of VTE was higher during the post-partum period than the ante-partum period. There was no significant difference in the incidence of fetal loss in the three groups, but this was not a primary endpoint. These results, obtained in a single center, have implications for VTE prophylaxis. Routine use of LMWH is not indicated during pregnancy in asymptomatic women with a single mutation. In contrast, it is justified throughout pregnancy in women with both mutations and a history of venous thrombosis. Regarding asymptomatic women with both mutations, the need for prophylaxis during part or all of the pregnancy should be weighed up on an individual basis. In the post-partum period, there is a consensus on the use of LMWH for 6 weeks in women with single or dual mutations associated with thrombophilia.

[Prevention of thrombo-embolic venous disease]. / Prophylaxie de la maladie veineuse thrombo-embolique.

Large epidemiological studies have shown that nearly all risk factors for deep vein thromboses have a different impact on the manifestation of the disease, which aids in their differentiation into high, moderate and low risk. North American authors have introduced a fourth class of very high risk. The prophylactic measures available are numerous. They can be used in isolation or association depending on the significance of the risk. In France, prophylaxis by LMWH (low molecular weight heparin) is by far the most frequently used method. Recently, apart from compression stockings and intermittent mechanical compression, the use of footpumps, and a technique of electrical calf stimulation have been proposed. Each thrombosis center or service should put in place a well defined strategy for prescribing thromboprophylaxis, adapted to the level of the thromboembolic risk for each group of patients. A dose of LMWH higher than that used for a moderate risk is indicated for most LMWH, in the case of a high or very high risk. A few problems still exist: the pre or postoperative timing of the first injection, the duration of the prophylaxis particularly during the post-discharge period, and the evaluation of the risk in certain situations such as laparoscopic surgery or limb immobilization, for which the studies are too few to formulate recommendations from the level of evidence available. The socioeconomic realities of using LMWH should not be ignored.

Assessment of apixaban plasma levels by laboratory tests: suitability of three anti-Xa assays. A multicentre French GEHT study.

While laboratory monitoring is not required in patients treated with apixaban, a direct factor-Xa inhibitor, assessment of its concentration is useful in some critical situations. However, few data are available on its effect on coagulation tests and on the suitability of anti-Xa assays for its quantification. It was the objective of this study to identify laboratory tests suitable for apixaban concentration assessment. Coagulation tests - PT and aPTT- and anti-Xa assays were performed in apixaban-spiked plasma samples. To evaluate the sensitivity of PT and aPTT to apixaban, we conducted a first monocenter part, with a wide range of concentrations (50-1,000 ng/ml), a large panel of reagents (20 reagents), and two coagulometers (STAR®, Stago and ACL TOP®, IL), and a second multicenter part involving 13 laboratories using either a common PT reagent (RecombiPlastin2G®) or the local PT and aPTT reagents. In the multicentre part, five blinded apixaban-spiked plasma samples (0/100/200/400/800 ng/ml - checked by HPLC-MS/MS) were used; apixaban concentrations were measured with three anti-Xa assays, apixaban calibrators and controls (Stago). PT and aPTT tests using a large panel of reagents displayed a low sensitivity to a wide range of apixaban concentrations. The concentrations to double PT ranged from 400 to >1,000 ng/ml with the 10 reagents. With the three anti-Xa assays, inter-laboratory precision and accuracy were below 11% and 12%, respectively. In conclusion, whereas PT and aPTT tests were not sensitive enough to detect apixaban, the three anti-Xa assays tested using lyophilised apixaban calibrators and controls allowed to reliably quantify a wide range of apixaban concentrations.