Global haemostasis and point of care testing

Anticoagulation Monitoring with Activated Partial ThromboPlastin Time and Anti-Xa Activity in Intensive Care Unit Patients: Interest of Thrombin Generation Assay

Current guidelines recommend monitoring the anticoagulant effect of unfractionated heparin (UFH) by measuring anti-Xa activity rather than activated partial thromboplastin time (aPTT) in intensive care unit (ICU) patients. The primary objective of this study was to evaluate the correlation of aPTT, anti-Xa activity, and thrombin generation in UFH-treated ICU patients. A prospective observational pilot study was conducted in adult surgical ICU patients treated with UFH. aPTT and anti-Xa activity were monitored daily. The therapeutic target was aPTT between 50 s and 84 s, and/or anti-Xa between 0.3 and 0.7 U/mL. Correlation among aPTT, anti-Xa activity, and thrombin generation was determined by measuring endogenous thrombin potential (ETP), with the inflammatory response evaluated. C-reactive protein (CRP) was used as a marker of inflammatory response. The plasma of 107 samples from 30 ICU patients was analyzed. The correlation between aPTT and anti-Xa activity was 0.66, CI95% [0.54;0.76] (p < 0.0001). Although thrombin generation, aPTT, and anti-Xa were correlated with inflammatory responses, the correlation was higher with thrombin generation and anti-Xa activity compared to aPTT. When aPTT was in a therapeutic range, a low thrombin generation was observed but was 50% inhibited when anti-Xa was in a therapeutic range. Coagulation testing with aPTT, anti-Xa correlated with thrombin generation. A 50% decrease in thrombin generation was observed when anti-Xa was within a therapeutic range. Further work is needed to evaluate coagulation biomarker responses and clinical outcomes in specific ICU populations.

[Thrombin generation assay in autoimmune disease]

Thrombin generation assay (TGA) is a useful tool to evaluate the initiation, propagation and inhibition of coagulation. TGA is a global test that is used to assess hemorrhagic risk in hemophilia patients, but it can also be used to study hypercoagulable states. The interest of TGA is to screen for cardiovascular risk, which is regularly associated with autoimmune disease (AID) such as antiphospholipid syndrome. Indeed, TGA has been used to evaluate hypercoagulability in patients with antiphospholipid syndrome treated with rivaroxaban versus warfarin. In other AIDs without thrombotic events, TGA measurement is elevated, mainly in rheumatoid arthritis (RA), systemic lupus erythematosus and Behçet's disease. These findings in RA are correlated with the inflammatory activity of the disease. In systemic lupus erythematosus and Behçet's disease, TGA appears to reflect disease activity. In conclusion, TGA remains relatively under used in the clinical evaluation of AID, but it could play a greater role in the evaluation of certain potentially thrombogenic treatments in AID. Finally, TGA helps measuring AID activity, due to the clearlink between coagulation and inflammation, despite some limitations of interpretation mainly due to a lack of standardization.

Overall hemostasis potential and aPTT-clot waveform analysis as powerful laboratory diagnostic tools for identification of hemophilia A patients with unexpected bleeding phenotype

INTRODUCTION

Traditionally used laboratory methods do not always accurately reflect bleeding severity in hemophilia A (HA) patients. The ability of three global assays for identifying patients with unexpected bleeding phenotype was investigated.

METHODS

Overall hemostasis potential (OHP), aPTT-clot waveform analysis (aPTT-CWA), endogenous thrombin potential (ETP), FVIII activities, and prothrombin fragment 1 + 2 concentrations were measured in 62 HA patients (30 severe and 32 non-severe) and 27 male controls. Bleeding phenotype was determined using our proposed scoring system including age at first joint bleed, number of target joints, and number of joint/muscle bleeds per year. Bleeding score ≤ 4 defined patients with mild bleeding phenotype (N = 27); score ≥ 5 defined severe bleeding phenotype (N = 35).

RESULTS

The receiver operating characteristic analysis performed for distinguishing patients with severe and mild bleeding phenotype yielded following values of area under the curve: 0.910 (FVIII); 0.891 (aPTT-CWA parameter DELTA); 0.769 (OHP); and 0.634 (ETP). Unexpected bleeding phenotype was identified in 11/62 HA patients: 8/32 (25%) non-severe HA patients had severe, while 3/30 (10%) severe HA patients had mild bleeding phenotype, and global assays enabled the identification of all these patients. OHP and DELTA were revealed as the most reliable parameters for bleeding phenotype determination (10/11 and 9/11 unexpected results, respectively).

CONCLUSION

This study emphasizes OHP and aPTT-CWA as a powerful laboratory diagnostic tool in identifying HA patients with unexpected bleeding presentations, with the best results achieved by combining both assays. Global assays should not completely replace FVIII activity measurement but should be a part of the HA diagnostic algorithm.

Bleeding and thrombotic complications of pediatric liver transplant

BACKGROUND

Pediatric patients undergoing liver transplant are at significant risk for bleeding and thrombotic complications due to the complex nature of rebalanced hemostasis in patients with liver disease.

METHODS/OBJECTIVES

We reviewed records of 92 pediatric liver and multivisceral transplant cases at Duke University Medical Center between January 2009 and December 2015. The goal was to define the nature and incidence of bleeding and thrombotic complications in this cohort and define potential risk factors.

RESULTS

There were 24 major bleeding events in 19 transplants (incidence 20.7%) and 30 thrombotic events in 23 transplants (incidence 25%). Five of the 10 retransplantations were for vascular thrombotic complications. Thirty-day mortality was 4.9%, and three of these four deaths were due to vascular thrombosis. No bleeding events led to retransplantation or mortality. Prophylactic aspirin was associated with decreased risk of thrombosis without increased bleeding. Prophylactic heparin did not increase bleeding risk. Laboratory assays predicted events poorly, apparently failing to capture the nuanced and dynamic interplay between pro- and anticoagulant factors in the posttransplant patient.

CONCLUSIONS

Both bleeding and thrombosis are frequent in this population, but only thrombotic complications contributed to retransplantation and mortality. A standardized approach to coagulation testing and antithrombotic therapy may be useful in predicting and reducing adverse outcomes. Alternative approaches to monitoring hemostasis need to be prospectively investigated in this complex patient population.

Thrombin generation potential and clot-forming capacity of thawed fresh-frozen plasma, plasma frozen within 24 h and solvent/detergent-treated plasma (octaplasLG® ), during 5-day storage at 1-6°C

To enable rapid availability of plasma in emergency situations, the shelf-life of thawed fresh-frozen plasma (FFP) has been extended from 24 h to 5 days. The aim of this study was to evaluate the thrombin generation (TG) potential and clot-forming ability during 5 days of refrigerated storage of thawed FFP, plasma frozen within 24 h and solvent/detergent-treated plasma octaplasLG® . During storage for 5 days, TG capacity decreased significantly over time, and rotational thromboelastometry showed significantly prolonged clotting times. However, the stability studies confirmed comparable in vitro haemostatic potentials of all three thawed plasma products at day 5.

Thrombin generation test: A reliable tool to evaluate the pharmacodynamics of vitamin K antagonist rodenticides in rats

Vitamin K antagonist rodenticide pharmacodynamics (PD) is studied in rodents with traditional laboratory tests. We wondered if thrombin generation test (TGT) could add value. Difethialone (10 mg/kg) was administered per os to 97 OFA-Sprague Dawley rats. PD was studied over a 72 h-period using the Calibrated Automated Thrombogram on platelet poor plasma before and after intoxication (3 female and 3 male rats for each 13 time points) and TGT parameters were compared with the prothrombin time (PT) and vitamin K dependent factor activities previously reported. Following intoxication, preliminary tests evidenced rapid and full inhibition of thrombin generation triggered with 5 or 20 pM human recombinant tissue factor. To study the evolution of TGT parameters following difethialone intake, we adapted the test by complementing intoxicated rat samples with pooled normal rat plasma (3/1, v/v). Adapted TGT confirmed the known higher procoagulant basal level in females compared to males through higher endogenous thrombin potential (ETP) and peak height (PH) (p < 0.0001 and p = 0.0003, respectively). An exponential model fitted well the PH and ETP decay after intoxication. In contrast to PT, the decreases were observed immediately following VKA intake and had comparable time to halving values: 10.5 h (95% CI [8.2; 13.6]) for ETP and 10.4 h (95% CI [7.8; 14.1]) for PH. The decrease of FVII and FX preceded that of PH, ETP and FII while FIX decreased later on, contributing to the severe hypo-coagulability. We demonstrated that TGT performed in samples of intoxicated rats complemented with normal plasma is a reliable tool for evaluation of VKA rodenticide PD in rats.

Comparative biochemical studies of fresh frozen plasma and pooled solvent/detergent-treated plasma (octaplasLG® ) with focus on protein S and its impact in different thrombin generation assay set-ups

BACKGROUND AND OBJECTIVES

The solvent/detergent treatment enables effective and robust inactivation of all lipid-enveloped viruses, but also inactivates partly sensitive plasma proteins such as protein S. The aim of this study was to investigate the thrombin generation capacity of octaplasLG^® , in particular focusing on the function of protein S in thrombin generation assay and the impact of assay settings.

MATERIALS AND METHODS

Sixteen octaplasLG^® batches and 32 units of single donor fresh frozen plasma (FFP) were investigated. For protein S, both functional activity and free antigen levels were measured. Thrombin generation assay was performed using two fluorogenic tests with different triggers. Finally, rotational thromboelastometry was performed.

RESULTS

Mean protein S levels were lower in octaplasLG^® , but a wider range of values was found for FFP. Clotting parameters and thrombin generation capacities overlapped between the two plasma groups as demonstrated using both thrombin generation assays and different triggers. Spiking studies with protein S-depleted plasma, human purified protein S or antibodies against protein S confirmed a correlation between protein S and thrombin generation capacity under specific assay conditions, especially in an assay with low tissue factor concentration.

CONCLUSION

Correlation between protein S and thrombin generation capacity was demonstrated in the TGA. Due to higher variability in protein S content in the FFP group, overlapping haemostatic potentials of the two plasma groups were found.

Global assays of hemostasis in the diagnostics of hypercoagulation and evaluation of thrombosis risk

Thrombosis is a deadly malfunctioning of the hemostatic system occurring in numerous conditions and states, from surgery and pregnancy to cancer, sepsis and infarction. Despite availability of antithrombotic agents and vast clinical experience justifying their use, thrombosis is still responsible for a lion’s share of mortality and morbidity in the modern world. One of the key reasons behind this is notorious insensitivity of traditional coagulation assays to hypercoagulation and their inability to evaluate thrombotic risks; specific molecular markers are more successful but suffer from numerous disadvantages. A possible solution is proposed by use of global, or integral, assays that aim to mimic and reflect the major physiological aspects of hemostasis process in vitro. Here we review the existing evidence regarding the ability of both established and novel global assays (thrombin generation, thrombelastography, thrombodynamics, flow perfusion chambers) to evaluate thrombotic risk in specific disorders. The biochemical nature of this risk and its detectability by analysis of blood state in principle are also discussed. We conclude that existing global assays have a potential to be an important tool of hypercoagulation diagnostics. However, their lack of standardization currently impedes their application: different assays and different modifications of each assay vary in their sensitivity and specificity for each specific pathology. In addition, it remains to be seen how their sensitivity to hypercoagulation (even when they can reliably detect groups with different risk of thrombosis) can be used for clinical decisions: the risk difference between such groups is statistically significant, but not large.

Consistency of thromboelastometry analysis under scrutiny: results of a systematic evaluation within and between analysers

While the use of thromboelastometry analysis (ROTEM®) in evaluation of haemostasis is rapidly increasing, important validity parameters of testing remain inadequately examined. We aimed to study systematically the consistency of thromboelastometry parameters within individual tests regarding measurements between different analysers, between different channels of the same analyser, between morning and afternoon measurements (circadian variation), and if measured four weeks apart. Citrated whole blood samples from 40 healthy volunteers were analysed with two analysers in parallel. EXTEM, INTEM, FIBTEM, HEPTEM and APTEM tests were conducted. A Bland-Altman comparison was performed and homogeneity of variances was tested using the pitman test. P-value ranges were used to classify the level of homogeneity (p<0.15 - low homogeneity, p = 0.15 to 0.5 - intermediate homogeneity, p>0.5 high homogeneity). Less than half of all comparisons made showed high homogeneity of variances (p>0.5) and in about a fifth of comparisons data distributions were heterogeneous (p<0.15). There was no clear pattern for homogeneity. On average, comparisons of MCF, ML and LI30 measurements tended to be better, but none of the tests assessed outperformed another. In conclusion, systematic investigation reveals large differences in the results of some thromboelastometry parameters and lack of consistency. Clinicians and scientists should take these inconsistencies into account and focus on parameters with a higher homogeneity such as MCF.