Prothrombin Time Reagents Research Articles

Continued harmonization of the international normalized ratio across a large laboratory network: Evidence of sustained low interlaboratory variation and bias after a change in instrumentation.

Our objective was to maintain low interlaboratory variation and bias in international normalized ratio (INR) results following a network change in instrumentation and reagents, using a process of ongoing standardization and harmonization. Network-wide standardization to new common instrument and reagent platforms followed by network-wide application of a simple novel process of verification of international sensitive index and mean normal prothrombin time values for each new lot of prothrombin time (PT) reagent that does not require use of World Health Organization reference thromboplastin or INR calibration/certified plasma. The network transitioned from mechanical hemostasis detection instruments with associated PT reagent (Diagnostica Stago; NeoPTimal) to optical detection (ACL TOPs) with associated PT reagent (Werfen; RecombiPlasTin 2G). Comparing 3 years of data for each situation, the network (n=27 laboratories) maintained low INR variability and bias relative to general mechanical and optical groups and other laboratories. Harmonized support for patient management of vitamin K antagonists such as warfarin was continuously maintained in our geography, with potentially positive implications for other coagulation laboratories and geographies. For the United States in particular, paucity of US Food and Drug Administration-cleared INR certified plasmas potentially compromises INR test accuracy; our novel approach may provide workable alternatives for other laboratories/networks.

International Council for Standardization in Haematology Field Study Evaluating Optimal Interpretation Methods for Activated Partial Thromboplastin Time and Prothrombin Time Mixing Studies.

The prothrombin time (PT) and activated partial thromboplastin time (APTT) are screening tests used to detect congenital or acquired bleeding disorders. An unexpected PT and/or APTT prolongation is often evaluated using a mixing test with normal plasma. Failure to correct ("noncorrection") prolongation upon mixing is attributed to an inhibitor, whereas "correction" points to factor deficiency(ies). To define an optimal method for determining correction or noncorrection of plasma mixing tests through an international, multisite study that used multiple PT and APTT reagents and well-characterized plasma samples. Each testing site was provided 22 abnormal and 25 normal donor plasma samples, and mixing studies were performed using local PT and APTT reagents. Mixing study results were evaluated using 11 different calculation methods to assess the optimal method based on the expected interpretation for factor deficiencies (correction) and noncorrection (inhibitor effect). Misprediction, which represents the failure of a mixing study interpretation method, was assessed. Percentage correction was the most suitable calculation method for interpreting PT mixing test results for nearly all reagents evaluated. Incubated PT mixing tests should not be performed. For APTT mixing tests, percentage correction should be performed, and if the result indicates a factor deficiency, this should be confirmed with the subtraction III calculation where the normal pooled plasma result (run concurrently) is subtracted from the mixing test result with correction indicated by a result of 0 or less. In general, other calculation methods evaluated that performed well in the identification of factor deficiency tended to have high misprediction rates for inhibitors and vice versa. No single method of mixing test result calculation was consistently successful in accurately distinguishing factor deficiencies from inhibitors, with between-reagent and between-site variability also identified.

PB1161 Evaluation of Three Prothrombin Time Reagents and their Sensitivity to Extrinsic Pathway Factor Deficiencies (FII, FV and FVII)

PB1161 Evaluation of Three Prothrombin Time Reagents and their Sensitivity to Extrinsic Pathway Factor Deficiencies (FII, FV and FVII)

Evaluation of newly-developed modified diluted prothrombin time reagent in non-valvular atrial fibrillation patients with direct oral anticoagulants: A comparative study with conventional reagents.

A single assay to assess the effect of the direct FXa inhibitor is needed clinically because prothrombin (PT) assay is not yet sensitive enough for accurate evaluation. We developed modified diluted prothrombin time (mdPT) assay showing a high reactivity to direct FXa inhibitors based on prothrombin time (PT) reagent. The purpose of this study was to evaluate the reactivity of mdPT to direct FXa inhibitors comparing to that of commercial PT reagents and diluted prothrombin time (dPT). The correlation and slopes of mdPT against the drug concentrations by anti-Xa assay were compared to those of the four commercial reagents of PT or dPT in 275, 257, and 243 clinical samples collected from non-valvular atrial fibrillation (NVAF) patients who are prescribed apixaban, edoxaban or rivaroxaban for stroke prevention, respectively. The correlation coefficient (95% confidence interval) of mdPT against apixaban, edoxaban, and rivaroxaban was 0.818 (0.775-0.854), 0.914 (0.892-0.932), and 0.814 (0.766-0.852), respectively. The slope (95% confidence interval) of mdPT for apixaban, edoxaban, and rivaroxaban was 0.0068 (0.0063-0.0075), 0.0076 (0.0072-0.0080), and 0.0072 (0.0065-0.0078), respectively, which were higher than that of four commercial PT and dPT reagents, ranging within 0.0006-0.0023, 0.0017-0.0038, and 0.0016-0.0057 (all, p < 0.001), respectively. Compared with other PT and dPT reagents, mdPT reagent showed sharper slope to all direct FXa inhibitors, and higher correlation to apixaban and comparable correlation to edoxaban and rivaroxaban. This new reagent is expected to be a coagulation screening assay having a consistently high response to any types of direct FXa inhibitors.

Pediatric Thromboelastograph 6s and Laboratory Coagulation Reference Values.

Specific reference intervals (RIs) facilitate accurate interpretation of results. Coagulation assay results may vary by demographics and also between reagents and analyzers used. Current Thromboelastograph 6s (TEG 6s) Hemostasis Analyzer RIs were generated from adult samples. To generate reagent analyzer-specific pediatric RIs for TEG 6s and coagulation parameters. A prospective, observational, single-center study of healthy children undergoing general anesthesia (January 3, 2017 to January 3, 2019). Venous blood samples were obtained for TEG 6s (Kaolin, Kaolin-Heparinase, Rapid and Functional Fibrinogen assays) and coagulation parameters (activated partial thromboplastin time, prothrombin time, thrombin clotting time, Echis time, antithrombin activity, and fibrinogen concentration using Instrumentation Laboratory ACL-TOP analyzers). Differences between activated partial thromboplastin time and prothrombin time reagents were investigated using mixed-effects regression, comparing maximum coefficients-of-variation with assay-specific allowable variation. RIs (lower/upper limits 2.5th of 97.5th percentiles) were generated using the following 2 methods: within discrete age-groups (neonates [<1 month], infants [1 month-1 year], young children [1-5 years], older children [6-10 years], and adolescents [11-16 years]), and modeled as functions of age and/or sex using quantile regression, including significant fractional polynomial and interaction terms. Variation between prothrombin time and activated partial thromboplastin time assays using different reagents was clinically significant. Reagent-analyzer specific pediatric RIs were generated using data from 254 children. Discrete and model-based RIs varied by age for all coagulation parameters and TEG 6s variables in all assays. We report reagent-analyzer specific pediatric RIs for TEG 6s and coagulation parameters. Observed variation reinforces recommendations for laboratory-specific RIs. These findings improve accuracy of interpretation of clinical results, provide a foundation for comparison and validation of tests in pathology, and illustrate feasibility and advantages of model-based RI approaches.

The mode of action of sugammadex on coagulation.

To explore the mode of action (MoA) by which sugammadex interferes with coagulation. The effect of sugammadex on various steps in the coagulation cascade including thrombin generation, factor Xa activity, and factor Xa generation was explored in human plasma. Sugammadex did not affect a conventional thrombin generation test (TGT), while it prolongs activated partial thromboplastin time (APTT) and prothrombin time (PT). However, a customized TGT with PT reagent revealed sugammadex effects. In addition, sugammadex prolonged a one-step prothrombinase-induced clotting time (PiCT) using human factor Xa. Furthermore, sugammadex interfered with factor Xa generation induced by an intrinsic and not by an extrinsic activator, nor by Russell's viper venom factor X (RVV-X). Adapted, rather than standard, experiments show that sugammadex is likely to decrease factor Xa activity in the common pathway and activation of factor X specifically in the intrinsic pathway.

Evaluation of STA-NeoPTimal, an extraction thromboplastin reagent with ISI close to 1.

The prothrombin time (PT) is the most requested test to investigate patients with congenital or acquired coagulopathies or to monitor oral anticoagulant therapy. However, thromboplastins can show markedly different responsiveness to the defects induced by vitamin K antagonist (VKA) therapy and are thus characterized by their ISI (International Sensitivity Index). INR results are optimal for patients under VKA but for patients screened for other reasons expressing PT results as ratio can be more appropriate. As it is very difficult to define the PT results reporting unit from the PT testing request, it would be ideal to use a thromboplastin with ISI=1. The study aims to compare our reference PT reagent with two candidate thromboplastins with ISI close to 1. We compared 3 different thromplastins: two rabbit brain extracted based reagents (STA-Neoplastine CI Plus, with ISI=1.26, routinely used in our laboratory and STA-NeoPTimal with ISI=1.01) and a recombinant thromboplastin (STA-Neoplastine R with ISI=0.97). The comparison was done on 175 samples: 75 from individuals without coagulation defects and 100 from patients under VKA. STA-NeoPTimal and STA-Neoplastine R well correlate to our reference, STA-Neoplastine CI Plus: regression equations are y=1.186x-0.1351, r2 =.9454 and y=1.1432x-0.1554, r2 =.9951, respectively. The lowest bias on INR results was obtained with STA-NeoPTimal reagent (interval: -0.7/+0.4). We conclude that STA-NeoPTimal can be used in the laboratory as it gives results comparable to those obtained with STA-Neoplastine CI Plus. Besides, thanks to its ISI=1, it guarantees reporting a PT ratio equal to INR which avoids errors.

Effect of anticoagulant adjustment on prothrombin time test using two different PT reagents in patients with elevated hematocrit

The recommendations for adjustment of citrate volume in sample tubes with high hematocrit (Ht) are based on indirect studies of underfilled tubes or artificially constructed Ht values. The aim of this study was to evaluate the effect of citrate volume adjustment in sample tubes from patients with hematocrit >55% using two different prothrombin time (PT) tests. MethodsPaired citrate-adjusted and unadjusted blood specimens were obtained from 181 patients from the pulmonary hypertension ambulatory with high Ht values and on warfarin therapy. The samples were tested using recombinant human tissue factor (RTF) and reagents extracted from rabbit brain (HS Plus). The results are expressed as the international normalized ratio (INR). The correlation and percent change (% change) between sample pairs were calculated. ResultsINR-RTF results from adjusted and unadjusted citrate blood specimens showed a strong correlation (R2 ​= ​0.8226, p ​< ​0.0001). The INR median was 2.25 (95% CI 2.10 to 2.41) for citrate-adjusted samples and was 2.22 (95% CI 2.06 to 2.38) for citrate-unadjusted samples. For samples with Ht >62%, the % change between sample pairs was >10%. Results using HS Plus showed a moderate correlation between citrate-adjusted and unadjusted samples (R2 ​= ​0.4267, p ​< ​0.0001). The INR median was 2.51 (95% CI 2.35 to 2.68) for citrate-adjusted samples and 3.45 (95% CI 3.11 to 3.80) for citrate-unadjusted samples. For samples with Ht>55%, the % change between sample pairs was higher than 10%. ConclusionOur data demonstrate that in patients with polycythemia on warfarin therapy, INR-RTF does not require anticoagulant adjustment for assessment of samples with Ht <62%.

Evaluation of a new thromboplastin reagent STA-NeoPTimal on a STA R Max analyzer for the measurement of prothrombin time, international normalized ratio and extrinsic factor levels.

We aimed at evaluating the performance of a new prothrombin time (PT) reagent (STA-NeoPTimal) with two other PT reagents (STA-Neoplastine R and STA-Neoplastine CI Plus) and the reference PT reagent used in our laboratory (ReadiPlasTin). Evaluation consisted in intra- and interassay precision assessment, determination of sensitivity to unfractionated heparin (UFH) or enoxaparin in spiked samples and to direct oral anticoagulants (DOACs) in patients (n=43). Method comparison of the 4 PT reagents, factor II, V, VII and X assays was tested on normal (n=20) and abnormal samples: VKA (n=47), preoperative (n=23), liver failure (n=12) and burned patients (n=37). Analytical performance met manufacturers' criteria for all reagents. All PT reagents gave correlation coefficients >0.8 and even >0.9 in many situations. In some VKA samples, differences≥0.5 INR units were found in samples within and above therapeutic ranges. For burned patients, PT correlations were good but with some minimal bias (<5.0%) while factor assays gave very consistent results (R>.8 and mainly >0.9). As expected, poor responsiveness of the PT to DOAC concentrations was observed with all four assays. The STA-NeoPTimal showed comparable performance to ReadiPlasTin, making it suitable for VKA control, detection of factors II, V, VII, X deficiency and assessment of liver disease coagulopathy. However, for patients receiving VKA, some significant differences were observed. We confirmed the inability of the PT assay to detect residual DOAC concentrations. Finally, burned patients results showed that recombinant thromboplastins were less sensitive to factor deficiencies in comparison to extraction thromboplastins.

The agreement between capillary and venous sampling for plasma PT/INR results

Regular measurement of prothrombin time (PT) as an international normalized ratio (INR) is of great importance in ensuring a safe Warfarin treatment due to the narrow therapeutic range. Hence, accurate results of the PT/INR analysis are crucial. Due to the high sampling load that patients on Warfarin experience, some prefer capillary sampling (from the tip of the finger) as an alternative to standard venous sampling (from the cubital fossa). The present study evaluated the method of capillary sampling compared to the standard venous method for plasma PT/INR measurement. Both venous and capillary samples were collected simultaneously for plasma PT/INR testing from 100 patients of which the majority undergoing active Warfarin treatment. The samples were analyzed on a Sysmex 2100i instrument (Siemens) using the Owrens method with PT reagents from MediRox. The capillary sampling method showed statistically significant lower values (p < .001) for plasma PT/INR than the standard venous sampling method with a mean difference (bias) of –0.14. It is improbable that the difference (bias) between capillary and venous sampling for plasma PT/INR analysis has clinical relevance. However, since the capillary blood collection and handling for plasma PT/INR is more technically demanding than the standard venous method we recommended that only specially trained personnel be entrusted to draw capillary blood for plasma PT/INR analysis.

Design and Utility of a Point-of-Care Microfluidic Platform to Assess Hematocrit and Blood Coagulation.

To develop a small volume whole blood analyzer capable of measuring the hematocrit and coagulation kinetics of whole blood. A co-planar microfluidic chamber designed to facilitate self-driven capillary action across an internal electrical chip was developed and used to measure the electric parameters of whole human blood that had been anticoagulated or allowed to clot. To promote blood clotting, select chip surfaces were coated with a prothrombin time (PT) reagent containing lipidated tissue factor (TF), which activates the extrinsic pathway of coagulation to promote thrombin generation and fibrin formation. Whole human blood was added to the microfluidic device, and voltage changes within the platform were measured and interpreted using basic resistor-capacitor (RC) circuit and fluid dynamics theory. Upon wetting of the sensing zone, a circuit between two co-planar electrodes within the sensing zone was closed to generate a rapid voltage drop from baseline. The voltage then rose due to sedimentation of red blood cells (RBC) in the sensing zone. For anticoagulated blood samples, the time for the voltage to return to baseline was dependent on hematocrit. In the presence of coagulation, the initiation of fibrin formation in the presence of the PT reagent prevented the return of voltage to baseline due to the reduced packing of RBCs in the sensing zone. The technology presented in this study has potential for monitoring the hematocrit and coagulation parameters of patient samples using a small volume of whole blood, suggesting it may hold clinical utility as a point-of-care test.

Dose-dependent effect of daptomycin on the artificial prolongation of prothrombin time in coagulation abnormalities: in vitro verification

BackgroundSeveral studies have reported that daptomycin induced artificial prolongation of prothrombin time (PT) in some test reagents, particularly in warfarin users. However, it remains unknown whether the artificial prolongation can be affected by coagulation abnormalities other than the use of warfarin. Thus, we investigated the effect of daptomycin on PT with two types of coagulation abnormalities.MethodsPlasma samples were pooled by four groups: healthy volunteers (Plasma A), warfarin users with a PT-international normalized ratio (INR) of approximately 2.0 (Plasma B) or 3.0 (Plasma C), and patients with liver cirrhosis with a PT-INR of approximately 2.0 (Plasma D). Plasma A was composed of plasma from two healthy individuals (9 mL from each individual). Plasma B, C, and D were composed of plasma from 36 patients (0.5 mL from each patient). Daptomycin was added to each sample to create solutions with several concentrations (0–150 μg/mL). The PT-INR for each solution was measured with three PT reagents. Linear regression analyses were used to determine the association between daptomycin concentration and PT-INR. The relative change in PT-INR due to daptomycin concentrations was calculated.ResultsStrong linear correlations were observed between daptomycin concentrations and PT-INR for all the plasma groups and reagents (R2 > 0.7, P < 0.01). At a daptomycin concentration of 150 μg/mL, the relative increase of PT-INR was ≥10% in the majority of the plasma groups with an elevated baseline PT-INR in all reagents tested.ConclusionsDaptomycin induced the artificial prolongation of PT-INR in a concentration-dependent manner, particularly in plasma samples with an elevated baseline PT-INR. PT should be evaluated at the trough levels of daptomycin.

A performance evaluation of a novel human recombinant tissue factor prothrombin time reagent (Revohem™ PT).

A new prothrombin time reagent (Revohem™ PT) based on recombinant human tissue factor produced by the silkworm-baculovirus expression system was tested. The aim of this study was to compare the performance of the new PT reagent with two widely used routine PT reagents. All testing was performed on a Sysmex CS-5100 coagulometer. Revohem™ PT was tested for imprecision and stability using normal and abnormal lyophilized commercial control plasmas. Comparability was assessed with two widely used reagents: one containing recombinant human tissue factor (Reagent A) and the other a human placental thromboplastin (Reagent B) using a wide range of normal and abnormal plasmas and analyser-specific ISI values. Excellent between-day imprecision was obtained for Revohem™ PT (CV <1.0%) and acceptable open-vial on-board stability over 7days. There was good agreement between methods in samples from patients with liver disease and patients receiving warfarin and no significant differences between methods with increasing INR values. Both recombinant reagents suffered less interference from lupus anticoagulant than the placental thromboplastin. Revohem™ PT had similar sensitivity to reagents A and B for FII, V, VII and X deficiency and demonstrated dose responsiveness to dabigatran, apixaban and rivaroxaban with steeper response curves than the comparison reagents. Revohem™ PT showed comparable or improved performance relative to two widely used reagents and is suitable for use in warfarin control, detection of inherited factor II, V, VII and X deficiency and assessment of liver disease coagulopathy.

Dose-dependent artificial prolongation of prothrombin time by interaction between daptomycin and test reagents in patients receiving warfarin: a prospective in vivo clinical study

BackgroundDaptomycin has been reported to cause artificial prolongation of prothrombin time (PT) by interacting with some test reagents of PT. This prolongation was particularly prominent with high concentrations of daptomycin in vitro. However, whether this prolongation is important in clinical settings and the optimal timing to assess PT remain unclear.MethodsA prospective clinical study was conducted with patients who received daptomycin for confirmed or suspected drug-resistant, gram-positive bacterial infection at a university hospital in Japan. PT at the peak and trough of daptomycin was tested using nine PT reagents. Linear regression analyses were used to examine the difference in daptomycin concentration and the relative change of PT-international normalized ratios (PT-INR).ResultsThirty-five patients received daptomycin (6 mg/kg). The mean ± standard deviation of the trough and peak concentrations of daptomycin were 13.5 ± 6.3 and 55.1 ± 16.9 μg/mL, respectively. Twelve patients (34%) received warfarin. With five PT reagents, a significant proportion of participants experienced prolongation of PT-INR at the daptomycin peak concentration compared to the PT-INR at the trough, although the mean relative change was less than 10%. None of the participants clinically showed any signs of bleeding. A linear, dose-dependent prolongation of PT was observed for one reagent [unadjusted coefficient β 3.1 × 10−3/μg/mL; 95% confidence interval (CI) 2.3 × 10−5–6.3 × 10−3; p = 0.048]. When patients were stratified based on warfarin use, this significant linear relationship was observed in warfarin users for two PT reagents (adjusted coefficient β, 6.4 × 10−3/μg/mL; 95% CI 3.5 × 10−3–9.3 × 10−3; p < 0.001; and adjusted coefficient β, 8.3 × 10−3/μg/mL; 95% CI 4.4 × 10−3–1.2 × 10−2; p < 0.001). In non-warfarin users, this linear relationship was not observed for any PT reagents.ConclusionsWe found that a higher concentration of daptomycin could lead to artificial prolongation of PT-INR by interacting with some PT reagents. This change may not be clinically negligible, especially in warfarin users receiving a high dose of daptomycin. It may be better to measure PT at the trough rather than at the peak daptomycin concentration.

Influence of apixaban on commonly used coagulation assays: results from the Belgian national External Quality Assessment Scheme.

The Belgian national External Quality Assessment Scheme performed a survey to assess the effect of the direct oral anticoagulant apixaban on the coagulation assays prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and antithrombin as performed with a large number of reagent/instrument combinations. Four lyophilized plasma samples spiked with apixaban (0, 41, 94 and 225 ng/mL) were sent to the 195 Belgian and Luxembourg clinical laboratories performing coagulation testing. PT and aPTT were barely influenced at the concentrations tested. At 225 ng/mL apixaban, PT and aPTT clotting times were only 1.15 times longer than at 0 ng/mL. Among PT reagents, RecombiPlasTin 2G® showed a slightly higher sensitivity with 225 ng/mL apixaban prolonging the PT clotting time 1.3-fold. Among aPTT reagents, there was no appreciable difference in sensitivity. Fibrinogen results were unaffected by the presence of apixaban, but antithrombin activity was considerably overestimated when measured with a FXa-based assay. At 225 ng/mL apixaban, the median percentage increase in antithrombin level was 31% when measured with the Liquid Antithrombin® reagent and 44% with the Innovance Antithrombin® reagent. Our data provide clinical laboratories with useful information on the impact of apixaban on their routine coagulation assays.

Laboratory monitoring of rivaroxaban and assessment of its bleeding risk

Background: The aims of this study were to investigate the effects of rivaroxaban on routine coagulation assays using our local, widely available, reagents and to study the relationship between sensitive coagulation assays and bleeding risk caused by rivaroxaban.Methods: Prothrombin time (PT), activated partial thromboplastin time (APTT) and anti-factor Xa (FXa) chromogenic assays (Biophen DiXaI) and inhibition of FXa activity were performed in normal pooled plasma (NPP) spiked with rivaroxaban and plasma samples from patients treated with rivaroxaban.Results: In vitro, the linear correlation coefficient of measured concentrations of rivaroxaban, by Biophen DiXaI, and spiked concentrations of rivaroxaban was 0.99. PT and APTT showed good linear correlation with rivaroxaban concentrations, while other assays showed poor correlation. In vivo, PT showed a moderate linear correlation with rivaroxaban concentrations while APTT had a weak correlation with rivaroxaban concentrations. In vitro and in vivo, the rivaroxaban concentrations, measured by Biophen DiXaI, always showed good correlation with the inhibition of FXa activity, and PT values showed moderate correlation with the inhibition of FXa activity.Conclusions: Biophen DiXaI can be considered as a quantitative method to monitor the anticoagulation activity of rivaroxaban, and could be used to evaluate bleeding risk caused by rivaroxaban. The PT reagent (Thrombosis S) could be considered as a rough method to monitor the anticoagulation activity of rivaroxaban and evaluate bleeding risk caused by rivaroxaban.

Prothrombin Time Tests for the Monitoring of Direct Oral Anticoagulants and Their Evaluation as Indicators of the Reversal Effect.

The prompt assessment and the reversal of direct oral anticoagulants (DOACs) are urgent matters in the emergency care setting. Thus, we planned to elucidate the adequate prothrombin time (PT) test for the evaluation of the anticoagulant effects of various DOACs. The anticoagulant effects of rivaroxaban, apixaban, and edoxaban were measured with 3 PT tests (Triniclot PT Excel S, Neoplastin R, and Thromborel S). Human plasma was spiked with each DOAC at a range of 0 to 1000 ng/mL, and the PT was measured using each PT test. In another series, the reversal effect of either 4-factor prothrombin complex concentrate (PCC) or activated PCC (aPCC) was evaluated with each PT test. All PT reagents correlated with the concentrations of each DOAC, however, the reactivity was considerably different between the DOACs and the PT tests. A prolonged PT with DOACs was reversed both by PCC and aPCC in a dose-dependent manner; however, Triniclot PT Excel S showed reprolongation of the PT with a higher dose of PCC. The proper choice of PT test is necessary for the assessments of the anticoagulant activity of DOACs. It is also important to understand the different characteristics of each PT test for the assessment of the reversal effects of PCC.

Anti-coagulation assessment with prothrombin time and anti-Xa assays in real-world patients on treatment with rivaroxaban.

Monitoring of anti-coagulation with the direct factor Xa inhibitor rivaroxaban is considered unnecessary in a routine clinical setting. However, assessment of its anti-coagulant effect may be desirable in certain clinical situations. We assessed prothrombin time (PT) reagents and commercially available anti-Xa assays (Biophen) calibrated for rivaroxaban and heparin in comparison to liquid chromatography-mass spectrometry (LC-MS/MS) measurements of rivaroxaban concentration in samples from patients on treatment with rivaroxaban for stroke prevention in atrial fibrillation. Citrate plasma samples were obtained from 30 randomly selected patients on uninterrupted treatment with rivaroxaban for a minimum of 1month. The anti-Xa assays, direct Xa inhibitor (DiXa-I®), and Heparin LRT® were conducted for both wide and low calibrations for rivaroxaban. Measurements were compared to LC-MS/MS using correlation, linear regression, intra-class correlation, and Bland-Altman analysis. In 30 patients (9 female) of median age 71.5years and BMI 26.5kg/m(2), rivaroxaban concentrations between 2.4 and 625ng/ml (median 82ng/ml) were measured by LC-MS/MS. PT reagents were poorly correlated with rivaroxaban concentrations (r (2) = 0.52 and 0.09). Anti-Xa assays DiXa-I (r (2) = 0.95) and Heparin LRT (r (2) = 0.97) were correlated with rivaroxaban in all concentrations, but especially in low concentrations with low calibrations (r (2) = 0.97 and 0.98, respectively). The highest agreement occurred between Heparin LRT and low rivaroxaban concentrations with a mean difference of -5.3ng/ml (limits of agreement, 12.9 to 2.4ng/ml). Anti-Xa assays can indirectly determine the concentration of rivaroxaban for a wide range of concentrations in real-world patients. An interpretation of anti-Xa and PT measurements in treatment with rivaroxaban requires knowledge of the local reagents.

Screening for hemostatic activities of popular Chinese medicinal herbs in vitro.

Aims:This study aimed to identify new hemostyptics by assessing the coagulation enhancing activity of 114 Chinese herbal extracts in vitro.Methods:Herbs were boiled in water for 30 min, filtered and then lyophilized filtrates (10 mg/mL) were dissolved in water. Coagulation was assayed as prothrombin time (PT). Plasma diluted in saline was incubated with each extract for 5 min and then PT reagent was added, followed by CaCl2 solution and the time taken to form clots was measured. Extracts that decreased coagulation time were regarded as containing active compounds. The abilities of extracts to activate Factor XII were assessed and the activated form of factor XII (XIIa) was resolved by SDS-PAGE and visualized by silver staining.Results:Coagulation time was obviously shortened by extracts of Alpinia Rhizome, Areca, Artemisia Leaf, Cassia Bark, Danshen Root, Ephedra Herb, Epimedium Herb, Forsythia Fruit, Great Burdock Achene, Moutan Bark, Perilla Herb, Red Paeony Root, Schizonepeta Spike, Senticosus Rhizome, Sweet Annie, Uncaria Thorn and Zanthoxylum Peel. Factor XII was obviously activated by extracts of Artemisia Leaf and Great Burdock Achene, and slightly by Perilla herb.Conclusion:Some popular Chinese medicinal herbs have potential as hemostatic agents and could thus be develope as new strategies for the treatment and prevention of bleeding.

Rivaroxaban Safety Threshold at 30 Ng/ml: Are a PT and/or a Aptt an Alternative to a Specific Test in the Real World?

The French Working Group on Perioperative Haemostasis (GIHP) published in March 2013 proposals for the management of major bleeding complications and emergency surgery in patients treated with direct oral anticoagulants, and especially the Rivaroxaban. This Direct Oral Anticoagulant (DOA) induces most of clotting tests, including Prothrombin Time (PT) and APTT. This led the GIHP to a degraded proposition for the institutions who does not propose the specific dosage of the molecule. This proposal assumes that the normality of the PT and aPTT exclude most patients with Rivaroxaban level >30 ng/ml. The aim of our evaluation is to verify the real-life practicability of this proposal.Samples from Rivaroxaban treated patients have been tested with 4 PT reagents: STA Neoplastine R (NeoR), STA Neoplastine CI+, Recombiplastine and Innovin. Four APTT reagents were also tested: STA-PTT automate, STA Cephascreen, Synthasil, Pathrontin SL. All reagents were tested on their specific analysers (STA-R, ACL TOP500, BCS XP). PT reagents were calibrated following manufacturer’s instructions (Stago, Instrumentation Laboratory, Siemens).Rivaroxaban prolongs PT but reagent’s sensitivity varies considerably and we observed a major individual variability, and this even at low Rivaroxaban concentrations. The NeoR presents the greatest sensitivity, the Innovin the lowest. For a normal PT (>70%), the NeoR alone can validly identify patients with Rivaroxaban level > 30ng/ml (sensitivity 93%). With the other reagents, from 42 to 51% of our patients with normal PT has Rivaroxaban level > 30 ng/ml. Two patients with Rivaroxaban > 150 ng/ml had normal PT with these 3 reagents. None of the APTT reagents has sufficient sensitivity to validly exclude these patients.In conclusion, none of the PT reagents can estimate Rivaroxaban concentration. The NeoR is the only reagent that allows distinguishing patients with residual Rivaroxaban level. For all other situations, specific test seems mandatory and the development of point-of-care system should be encouraged. DisclosuresNo relevant conflicts of interest to declare.