ALBERT

Description: Introduction: Ponatinib is a BCR-ABL tyrosine kinase inhibitor (TKI) indicated in adult patients suffering from chronic myeloid leukemia (CML) or “Philadelphia-chromosome positive” (Ph+) acute lymphoblastic leukemia resistant or intolerant to dasatinib or nilotinib. A high incidence of arterial events including peripheral artery occlusive diseases has been observed with ponatinib during the clinical development. A similar risk was also suspected with nilotinib, another BCR-ABL TKI used in CML. To date, no signal of increased risk of vascular thrombosis and embolism was found in clinical trials with imatinib and dasatinib. However, some cases were reported post-marketing. Aim: To perform a meta-analysis to assess the risk of vascular occlusive events (VOE) with novel generation BCR-ABL TKI (i.e. bosutinib, dasatinib, nilotinib and ponatinib) in CML patients compared with standard of care (i.e. imatinib). Stratifications by BCR-ABL TKI are performed to provide product specific risk assessment. Data on the overall survival and the major molecular response were also extracted to provide global benefit-risk evaluation. Methods: Study selection was performed in two stages. Initially, two independent reviewers screened abstracts and titles against inclusion and exclusion criteria (see protocol at PROSPERO 2014:CRD42014014147). Then, both reviewers assessed potentially relevant papers in their entirety, deciding on inclusion. Studies included all randomized controlled trials (RCT), comparing BCR-ABL TKI versus the reference therapy. Data on major molecular response, overall survival and VOE were extracted. The meta-analysis was performed using a fixed-effect model. Odds ratios (OR) with 95% confidence intervals (CI) were computed using the Peto method. Statistical heterogeneity across the various trials was tested using the Cochran's Q statistic and quantified by the I2 value. Funnel plot asymmetry was assessed by the method of Egger's linear regression, the Begg and Mazumbar rank correlation and the Owrin's fail safe N tests. Results: Among the 10 studies included, 3 studies did not report overall survival and 9 studies reported VOE and the major molecular response. Risk of VOE was increased with dasatinib (OR 3.86; 95%CI: 1.33 to 11.18), nilotinib (OR: 3.45; 95%CI: 2.07 to 5.63) and ponatinib (OR: 3.47; 95%CI: 1.23 to 9.78) compared to imatinib in patients with Ph+ CML (Figure 1). No significant difference was found with bosutinib (OR: 2.77; 95%CI: 0.39 to 19.77) probably due to a lack of power, but a trend was also demonstrated (Figure 1). Novel generation TKI increased the rate of major molecular response at 1 year compared to imatinib (overall OR: 2.22; 95%CI: 1.87 to 2.63) (Figure 2). No statistical difference in term of overall survival at one year was found (overall OR: 1.23; 95%CI: 0.67 to 2.23) (Figure 3). Unfortunately, the inaccessibility to individual data and to the time-to-event along with the fact that the evaluation criteria were not similar between studies can introduce a bias in the analysis. However, neither heterogeneity nor publication bias were found, supporting the robustness of our results. The risk of VOE is likely to be dose-related; however, currently available data on dose-efficacy and dose-toxicity relationship are not sufficient to make a formal recommendation on dose reduction, since there is a risk that lower doses might have reduced efficacy. However, safety and efficacy data concerning dose reduction following major cytogenetic response have been included in the EU-SmPC of Iclusig¨ (ponatinib) as a risk minimization measure. Conclusion: Dasatinib, nilotinib and ponatinib increase VOE. Novel generation TKI improve major molecular response but not the overall survival at one year. Further dose-ranging studies are required to define the dose regimen of each BCR-ABL TKI that will provide the best benefit-risk profile. Monitoring the response at the individual level might be of utmost importance to reduce the risk of VOE while keeping the benefit in term of major molecular response. Figure 1. Forest plot of the risk of VOE in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Figure 1. Forest plot of the risk of VOE in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Figure 2. Forest plot of the major molecular response in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Figure 2. Forest plot of the major molecular response in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Figure 3. Forest plot of the overall survival in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Figure 3. Forest plot of the overall survival in patients with Ph+ leukemia treated with new generation TKIs versus imatinib. Disclosures Graux: Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Description: Introduction There is still a need for a general test easily implementable and widely available that may be used to screen all patients on DOACs. A recent study has suggested that the dilute Russell Viper Venom Time (DRVV-T) could be used for the monitoring of DOACs but these results have been generated in vitro. The primary objective of this study is to analyse and compare the results obtained with the DRVV Screen and Confirm tests to the plasma drug levels measured by LC-MS/MS. We also aimed at proposing specific cut-off associated with supratherapeutic levels at Ctrough. Finally, a comparison of our results with those obtained with PT for rivaroxaban and aPTT for dabigatran is also provided. Methods Thirty-two rivaroxaban and 31 dabigatran platelet poor plasma samples from real-life patients were included in the study. Dilute Russell's Viper Venom time was measured using STA®-Staclot®DRVV Screen and Confirm reagents. Prothrombin Time and aPTT have been performed with Triniclot PT Excel S® and RecombiPlastin 2G® and with STA®C.K. Prest and SynthasIL®, respectively. The Hemoclot Thrombin Inhibitor® and the Biophen DiXaI® have been performed to estimate plasma concentration of dabigatran and rivaroxaban, respectively. All methodologies were performed on a STA-R Evolution® analyser according with the recommendation of the manufacturer, except for RecombiPlastin 2G® which were performed on an ACL-TOP®. All of these tests have been performed according to the recommendations of the manufacturer. The reference LC-MS/MS measurement of plasma drug concentrations were validated according to FDA Guidelines for Industry for Bioanalytical Method (for rivaroxaban) and to the Validation European Medicines Agency guidelines (for dabigatran). Results The plasma concentrations range from 6 to 426ng/mL for rivaroxaban and from 0 to 386ng/mL for dabigatran as determined by LC-MS/MS. Tables 1 and 2 summarize Spearman correlations and Bland-Atlman analyses for rivaroxaban and dabigatran, respectively. Figures 1 and 2 provide the results of STA®-Staclot®DRVV Screen and Confirm versus LC-MS/MS measurements. Bland-Altman graphs are also provided. Discussion STA®-Staclot®DRVV-Screen and Confirm shows a better correlation than PT or aPTT. Bland-Altman analyses reveal an overestimation of approximately 40ng/mL and large 5th-95th limits of agreement with both STA®-Staclot®DRVV-Screen and Confirm. Specific cut-offs associated with supratherapeutic level (〉200ng/mL) at Ctrough have been defined. For STA®-Staclot®DRVV-Screen, results below 125 seconds or below a ratio of 3 could exclude plasma concentrations 〉200ng/mL for rivaroxaban and dabigatran (Figure 1 - A and B). For STA®-Staclot®DRVV-Confirm, cut-offs must be adapted independently (Figure 2 - A and B). Results below 75 seconds or below a ratio of 2, could exclude rivaroxaban plasma concentrations 〉200ng/mL. For dabigatran, the threshold could be defined at 90 seconds or at a ratio of 2.5. Conclusion Thanks to its good correlation with plasma drug level, DRVVT can be more informative than PT and aPTT, to exclude supra-therapeutic level of rivaroxaban and dabigatran at Ctrough. However, due to overestimations in plasma drug level, it cannot be recommended to accurately estimate plasma drug concentrations which require more specific coagulation assays or LC-MS/MS measurements. Disclosures: No relevant conflicts of interest to declare.

Description: Introduction Dabigatran etexilate (DE) is an oral direct thrombin inhibitor approved for prevention of stroke and systemic embolism in adult patients with non-valvular atrial fibrillation (NVAF). In the RE-LY trial, myocardial infarction (MI) rates were increased with DE 110mg bid and 150mg bid when compared to warfarin. The risk of MI associated with the use of DE was assessed in a previous meta-analysis of 7 non-inferiority randomized controlled trials (RCTs) showing a significant 33% increase in MI. We performed an updated meta-analysis of RCTs comparing DE with active comparators or placebo to assess the effect of this agent on MI risk as a primary objective. The outcome of major bleeding (MB) and all-cause mortality was also assessed to provide global safety and efficacy measure. Stratifications by comparators (enoxaparin, warfarin or placebo) and by studies using the 150mg bid and the 110mg bid dose regimen were performed. Materials and Methods We conducted searches of the published literature and a clinical-trials registry maintained by the drug manufacturer till 22th of March, 2013. Criteria for inclusion in our meta-analysis included all RCTs and the availability of outcome data for MI, MB and all-cause mortality. Among the 423 unique references identified, 13 RCTs fulfilled the inclusion criteria. All methodologies were performed according to the PRISMA Statement. Results Myocardial infarction occurs in 287 of 23,839 patients (1.20%) treated with DE and in 106 of 13,536 patients treated with controls (0.78%). Major bleeding occur in 948 of 27,063 patients (3.50%) treated with DE and in 551/15,341 patients (3.59%) treated with controls. Death occurs in 989 of 24,162 patients (4.09%) treated with DE and in 570 of 14,498 patients (3.93%) treated with controls. Overall OR for MI, MB and all-cause mortality were 1.32 (95% CI; 1.07-1.63; P=0.010), 0.85 (95% CI: 0.79-0.98; P=0.010) and 0.90 (95% CI; 0.81-1.00; P=0.046) (Figure 1). When compared to warfarin, OR for MI, MB and all-cause mortality were 1.38 (95% CI: 1.08-1.77; P=0.010), 0.85 (95% CI: 0.75-0.95; P=0.006) and 0.90 (95% CI: 0.81-1.01; P=0.069), respectively (Figure 1). In RCTs using the 150mg bid dose regimen, OR for MI, MB and all-cause mortality were 1.44 (95% CI: 1.09-1.90; P=0.010), 0.92 (95% CI: 0.81 to 1.05; P=0.228) and 0.88 (95% CI: 0.78-1.00; P=0.045), respectively (Figure 2). Results of the 110mg bid dose were mainly driven by the RE-LY trial. Discussion DE significantly reduced MB and all-cause mortality compared to controls. However, while the reduction of MB is statistically significant versus warfarin, the reduction in all-cause mortality is not (Figure 1B & 1C). The increased risk of MI with the 150mg bid dose is significant but the reduction in MB and mortality is non-statistically significant (Figure 2). Taken together, these remarks suggest that in frail patients presenting comorbidities, the choice of the 150mg bid dose should be carefully discussed and the 110mg bid dose might be considered. Based on our results, one cannot conclude that the 110mg bid dose is associated with a higher risk of MI. However, in terms of absolute risk, such an increased risk of MI should be tempered when compared to the outcomes of stroke or systemic embolism, MB and all-cause mortality. The results from the RE-LY trial showed that the benefits of DE over warfarin outweigh this increase risk of MI. The risk difference was greatly in favor of DE regarding the composite of stroke/systemic embolism, MI, MB and all-cause mortality. Conclusion This meta-analysis of RCTs provides robust evidence that DE is associated with an overall significant 32% increase in the risk of MI. The risk was principally identified when warfarin is used as comparator (38% increase). In RCTs using the 150mg bid DE dose, a significant 44% overall increased risk of MI was identified. No definitive conclusion about the absence of the risk of MI with the 110mg bid DE dose can be drawn at this time. However, this increase risk has to be tempered with the overall benefit of DE especially in the patients with NVAF. In conclusion, we suggest that health care professionals and regulators should consider additional risk minimization strategy to prevent the risk of MI in vulnerable population. Disclosures: No relevant conflicts of interest to declare.

Description: BACKGROUND Dabigatran etexilate has received its market authorization for various indications worldwide. It was developed to be used in fixed dose regimens without the need of regular monitoring. However, the perioperative management of dabigatran could require an assessment of the drug plasma levels to ensure a safe use of the product, especially in absence of specific antidotes. The EMA stated that dabigatran concentrations under 48 ng/mL should be reached before invasive intervention. The GIHP put the threshold at 30 ng/mL. Therefore, a specific laboratory assay, accurate in the low concentration range, easily available and performable 24h/7 is requested but, until now, all coagulation tests dedicated to the measurement of plasma dabigatran concentrations showed a lower limit of quantitation from 30 to 50 ng/mL. This limits their perioperative utility and the thrombin time (TT) is currently presented as an alternative due to its very high sensitivity to dabigatran. This interesting approach has limitations because TT is affected by several analytical and biological variables that could lead to misinterpretations and expose the patient at riskier hemostatic conditions. In this study, we propose to investigate the performance of two coagulation tests (the Hemoclot Thrombin Inhibitors LOW (HTI LOW) (Hyphen BioMed) and the Ecarin Chromogenic Assay II (ECA-II) (Diagnostica Stago)) specifically developed to measure low plasma dabigatran concentrations and to compare their results with a reference LC-MS/MS. We also assessed the performance of the standard procedure of HTI and TT. MATERIALS AND METHODS Thirty-three plasma samples of patients treated with dabigatran etexilate for stroke prevention in non-valvular atrial fibrillation, were included in the study. Plasma samples were taken randomly and included after a first screening using the HTI to select plasma concentrations

Description: Abstract 1169 INTRODUCTION: New oral anticoagulants (NOACs) have been recently approved by the European Medicine Agency (EMA) and the Food and Drug Administration (FDA) for several indications. New oral anticoagulants include anti-IIa agent (dabigatran etexilate) and anti-Xa agents (rivaroxaban, apixaban and edoxaban). NOACs do not require monitoring nor frequent dose adjustment. However, searching for the optimal dose in the individual patient may be useful in some situations. Recent studies have shown that aPTT, HTI and ECT could be used to monitor dabigatran whereas PT and anti-Xa chromogenic assays could be used to monitor anti-Xa agents, while standardizing the time between the last intake of rivaroxaban and the sampling is mandatory. These tests only measure the initiation phase of the coagulation cascade. Thrombin generation assay (TGA) which measures the entire thrombin generation process could be used to better discriminate the inhibitory profile of the NOACs in patients. OBJECTIVES: To study the impact of dabigatran and rivaroxaban in patients by thrombin generation assay compared to other traditional coagulometric and chromogenic assays. MATERIALS AND METHODS: Five patients under dabigatran and 5 patients under rivaroxaban for atrial fibrillation were included in this study. Blood samples were taken at different intervals: at Ctrough, 2h and 3h after drug administration. The following tests were performed at each timepoint Rivaroxaban: Prothrombin Time (PT) using the following reagents: Triniclot PT Excel S.. and Innovin.., Thrombin Generation Assay (TGA) using PPP-Reagent and PPP-Reagent High, Biophen Direct Factor-Xa Inhibitor.. (DiXaI). Dabigatran: Activated Partial Thromboplastin Time (aPTT) using CK-Prest.. and Synthasil.., Hemoclot Thrombin Inhibitor.. (HTI) and Thrombin Generation Assay (TGA) using PPP-Reagent and PPP-Reagent Low. All the tests were calibrated by spiking rivaroxaban or dabigatran at increasing concentrations in pooled citrated normal human platelet poor plasma (PPP). RESULTS AND DISCUSSIONS: In vitro Rivaroxaban The Peak and mVRI were the most sensitive CAT parameters with a high sensitivity (Peak IC50 was 3ng/mL with PPP-Reagent Low and PPP-Reagent and 14ng/mL with PPP-Reagent High; mVRI IC50 was 1ng/mL with PPP-Reagent Low and PPP-Reagent and 3ng/mL with PPP-Reagent High) and both reagent showed a low variability (CV

Description: Abstract 2275 Introduction: Apixaban is direct factor-Xa inhibitor that reached the market for the prevention of venous thromboembolism in patients undergoing major orthopaedic surgery. It is also being evaluated in the reduction of recurrent ischemic events when added to antiplatelet therapy after an acute coronary syndrome and in the prevention of stroke in patients with non-valvular atrial fibrillation. Thanks to its predictable pharmacokinetic profile, biological monitoring is not required. Nevertheless, evaluation of plasma drug concentration may be valuable in specific situations such as recurrent thrombosis, bleedings, before urgent surgery, in case of bridging and in case of at least two risk factors among the following ones: drug interactions with caution, moderate renal impairment and moderate hepatic impairment; Monitoring may also be useful in infants, pregnant women or in extreme body weights, although no relevant data on drug levels associated with approximate therapeutic and harmful ranges are currently available. Material and Methods: Apixaban was spiked at increasing concentrations (0, 5, 10, 20, 50, 100, 200 and 500 ng/mL) in pooled citrated normal human platelet poor plasma (PPP) to measure Prothrombin Time (PT) and dilute PT with different thromboplastin, Thrombin Generation Assay (TGA) with different inducers and activity on different anti-Xa chromogenic assays. Activated Partial Thromboplastin Time with different reagents, Thrombin Time (TT), Ecarin Clotting Time (ECT) and Reptilase Time (RT), measurement of fibrinogen (Clauss method and PT-derived method) and antithrombin (anti-IIa and anti-Xa based chromogenic assays) were also tested. We also evaluated the impact of apixaban on assays used for the determination of lupus anticoagulant such as the DRVV-T.. (Screen and Confirm) as well as the PTT-LA.. and the Staclot-LA.. . Results and Discussion: As mentioned in previous studies, PT showed a weak sensitivity towards apixaban in comparison with the plasma range obtained in short pharmacokinetic studies. Indeed, the concentration needed to double the clotting time was 154 ng/mL with the most sensitive reagent while the mean Cmax obtained in a short PK study after one oral intake of 5 mg apixaban (dose given in atrial fibrillation) was 96 ng/mL. Therefore, the sensitivity of PT is not strong enough to allow accurate quantitative measurement of the plasma drug concentration (Table 1). Activated Partial Thromboplastin Time presented a better sensitivity but showed a plateau after 100 ng/mL reflecting the uselessness of this test for the quantification of apixaban. Thrombin Time, ECT and RT were logically not affected while DRVV-T.. showed a sensitivity of 205 ng/mL (Screen), which is once again not enough sensitive. On the opposite, chromogenic anti-Xa assays seemed to be very sensitive (Figure 2 and Table 1). Nevertheless, the relation was not always linear and some methodologies needed to be adapted to ensure a broader range of application. TGA (Figure 1) may be useful to assess the pharmacodynamics effects of apixaban on the coagulation process. Nevertheless, the turn around time and the lack of standardisation are currently limitations that restrict the use of this method. In the case of the exploration of an haemorrhagic event, specific tests such as RT, fibrinogen (Clauss and PT-derived method (dFib)), TT and clotting factor activity may be used. Apixaban did not interfere with these tests. Antithrombin determination if also of importance and chromogenic anti-IIa based assays should be used in face of patients treated with apixaban to avoid misdiagnosis since an overvaluation of 12% by 100 ng/mL was shown using one chromogenic anti-Xa based assay. Conclusion: PT may not be used as screening test to assess the risk of bleedings. A more specific and sensitive assay such as chromogenic anti-Xa assays using calibrators should be used to correctly assess the concentration of apixaban. Determination of lupus anticoagulant using DRVV-T.. and PTT-LA.. or Staclot LA.. as well as the determination of antithrombin using factor-Xa based chromogenic assays, were influenced by apixaban. Finally, standardization of the time between the last intake of apixaban and the sampling is mandatory. Figures: Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 3332 Introduction: Recently, 2 oral anticoagulants have been marketed: dabigatran, a direct thrombin inhibitor, and rivaroxaban, a direct FXa inhibitor. Thanks to their safety and efficacy profiles, routine coagulation monitoring is generally not required. However, the most commonly reported adverse reactions with these drugs are bleedings. A sensitive laboratory assay might be valuable to measure the pharmacodynamics of these 2 drugs in different situations including risks of drug interaction (i.e. strong P-gp inhibitors), overdose or to measure patient compliance. Due to their different mechanism of action, the measurement of their anticoagulant level in plasma may require different types of clotting assays. Aims: The aim of the present study was to determine which coagulation assay(s) could be used to measure the impact of rivaroxaban and dabigatran among a range of routine or more specific tests. Methods: Both drugs were spiked at increasing concentrations in pooled citrated normal human platelet-poor plasma (PPP). The final concentrations were ranging from 10 nM to 2 μM for dabigatran and from 25 nM to 5 μM for rivaroxaban. Such concentrations covered the plasma range in patients during orthopedic surgery. The following routine clotting assays were performed with the spiked plasma according to the manufacturer's protocols: Prothrombin Time (PT) with Neoplastin CI+ and Neoplastin R on STA-R (Roche Diagnostics), with Innovin on BCS (Siemens) and with Recombiplastin on ACL-TOP (Instrumentation Laboratories); activated Partial Thromboplastin Time (aPTT) with CK-Prest, PTT-A and Cephascreen on STA-R, with Actin FS on BCS and with Synthasil on ACL TOP and Thrombin Time (TT) on STA-R. More specific tests included Prothrombinase-induced Clotting Time (PiCT, Pefakit®, Pentapharm) and Ecarin Clotting Time (ECT) on STA-R; dilute PT (dPT) and activated Clotting time (ACT) on KC10. Thrombin Generation Tests (TGT) were also performed with Calibrated Automated Thrombogram (CAT) using PPP or PPP LOW reagents (Thrombinoscope). Sensitivity of a coagulation assay was defined as the concentration required to double clotting time (2XCT). Results: Dabigatran. A concentration-dependent prolongation of PT, dPT and aPTT was observed. However, at high concentrations, sensitivity of aPTT decreased whereas sensitivity of PT increased. The results varied depending on the clotting reagent used. TT was too sensitive leading to high variability for concentrations higher than 250nM. PiCT showed a linear concentration coagulation time (CT) relationship until a plateau at 750nM. ECT showed a high sensitivity (2X CT ≈ 93 nM), a linear relationship in the whole concentration range and a very low variability (CV≤ 1,8%). ACT gave a similar profile to PT (Innovin) with a slightly higher sensitivity (2X CT ≈ 716 nM vs 842nM). Dabigatran induced a concentration-dependent delay and inhibition of the tissue factor-induced thrombin generation with 5 pM TF or 1 pM TF with 4 μM PL and 16.7 mM CaCl2. The drug strongly increased the lag time and Tmax whereas it slightly decreased the Cmax and ETP. The lag time was the most sensitive CAT parameter with a high sensitivity (2x lag time ≈ 145 nM) and a low variability (CV≤6%). Rivaroxaban. A concentration-dependent prolongation of PT, dPT and aPTT was observed. However, at high concentrations, sensitivity of aPTT increased. Sensitivity of dPT (2X CT ≈ 109 to 550 nM) and PT (2X CT ≈ 138 to 764 nM) were similar and superior to aPTT (2X CT ≈ 897 to 2050 nM). The results varied depending on the clotting reagent used. TT was insensitive to rivaroxaban until 2500nM. Both PiCT and ECT showed a low sensitivity (2X CT ≈ 2536 nM and 5750 nM, respectively). A concentration-dependent prolongation of ACT was observed until 2500nM (2X CT ≈ 2275 nM). Rivaroxaban induced a concentration-dependent reduction and delay of the TF-induced thrombin generation. The Cmax was more strongly decreased than the ETP whereas the Tmax was more prolonged than the lag time, showing a major influence on the amplification phase. The Cmax was the most sensitive CAT parameter with a high sensitivity (Cmax EC50 ≈ 50 nM) and a low variability (CV

Description: Introduction Possibilities to monitor the intensity of dabigatran etexilate (DE) treatment may be valuable before urgent intervention. The Working Group on Perioperative Haemostasis proposed that the drug plasma concentration ([]) should be less or equal to 30ng/mL. However, plasma levels where it is safe to carry out an invasive procedure or surgery have not been confirmed prospectively. In addition, no biological test has been correlated with bleeding risk. Literature showed heterogeneous data regarding the arrest of DE depending on the renal function and the haemorrhagic risk. In addition, physicians request guidance for patients excluded from the clinical trials. Consequently, there is still a need for a rapid and widely available biological test. Some authors make proposals based on activated Partial Thromboplastin Time (aPTT), Hemoclot Thrombin Inhibitor® (HTI) or Thrombin Time (TT). TT displayed several advantages over aPTT. However, TT is affected by numerous analytic variables. Therefore, the objectives of the present study were: 1. To determine the optimal [thrombin] with a variety of instruments and reagents 2. To assess the repeatability of TT at optimized conditions 3. To compare the sensitivity and linearity of TT at residual [dabigatran] (DA) with those of aPTT and HTI 4. To validate the fibrinogen reagent (with heparin inhibitor) for TT experiments Methods DA was spiked at increasing [] in pooled citrated normal human platelet-poor plasma (NPP). The following [DA] were prepared: 0, 5, 10, 20, 30, 40 and 50ng/ml. 1. Optimal [thrombin] determination. The optimal [thrombin] was defined with 2 reagents: bovine thrombin (HemosIL® TT) and human thrombin (STA®-Thrombin) on 4 instruments: STA-R Evolution®, ACLTOP® , CS2000i® and KC10®. TT higher than Tmax is not informative for the physician. Thus the optimized [thrombin] was defined as the maximum [] giving, in a reproducible way, a TT at 50ng/ml lower than Tmax and a TT at 0ng/ml higher than the minimum TT. The Tmax was set arbitrarily at 120 sec. 2. Repeatability The repeatability of optimized TT was assessed by running aliquots of NPP spiked with all [DA] on 10 consecutive days 3. TT (1.5 NIH/ml, STA®-Thrombin), aPTT with SynthasIL® and STA®-C.K.Prest, and HTI were also determined within 1 hour on STA-R® on replicates of all NPP solutions. 4. STA®- Fibrinogen-5 was diluted to the optimized [thrombin] (1.5 NIH/ml) on STA-R® and used as a thrombin reagent. Results 1. The thrombin origin is a more important variable in comparison to the type of coagulometer. At [DA] of 30ng/ml and [thrombin] of 1.5 NIH/ml, the STA®-TT ranges from 56 sec to 74 sec according to the instrument, whereas on a same instrument, the TT varied of minimum 43 sec, depending on the thrombin origin. The optimized [thrombin] are the following : a) STA-R®, STA®-Thrombin : 1.5 NIH/ml, b) STA-R®, HemosIL® TT : 3.8 NIH/ml, c) ACLTOP®, STA®-Thrombin 3.8 NIH/ml, d) ACLTOP®, HemosIL® TT 5.0 NIH/ml, e) KC10®, STA®-Thrombin 1.5 NIH/ml, f) KC10®, HemosIL® TT 5.0 NIH/ml, g) CS2000i®, STA®-Thrombin 1.4 NIH/ml, h) CS2000i®, HemosIL® TT 3.8 NIH/ml. Except for STA®-Thrombin on STA-R®, the [optimized] is not the one recommended by the manufacturer. Figure 1 shows the results of optimized TT according to thrombin origin and coagulometer. 2. Repeatability experiments showed that variability increased with the [DA] (i.e. STA®-Thrombin (STA-R®): coefficient of variation: 8.0% and 28.9% for 0ng/ml and 50ng/ml, respectively) and that the variability depends on the coagulometer and the reagent. 3. Comparison of sensitivity and linearity of TT, aPTT and HTI are presented in Table 1. APTT is not sensitive enough in low [DA], whatever the reagent, whereas HTI is not suitable in [DA] lower than 50ng/ml. 3. TT performed with fibrinogen reagent shows longer times in comparison to thrombin reagent (〉120 sec vs 109 sec at 30ng/ml DA). Conclusions TT may be more informative than aPTT and HTI to provide with guidance to carry out an urgent procedure or surgery for patients receiving DE. However, TT is affected by a lot of analytic variables that should be understood by laboratories. Each laboratory should optimize its TT procedure according to its combination coagulometer-reagent. Disclosures: No relevant conflicts of interest to declare.