Sean Platton

Functional definition and characterization of acute traumatic coagulopathy.

Objective:To identify an appropriate diagnostic tool for the early diagnosis of acute traumatic coagulopathy and validate this modality through prediction of transfusion requirements in trauma hemorrhage. Design:Prospective observational cohort study. Setting:Level 1 trauma center. Patients:Adult trauma patients who met the local criteria for full trauma team activation. Exclusion criteria included emergency department arrival >2 hrs after injury, >2000 mL of intravenous fluid before emergency department arrival, or transfer from another hospital. Interventions:None. Measurements:Blood was collected on arrival in the emergency department and analyzed with laboratory prothrombin time, point-of-care prothrombin time, and rotational thromboelastometry. Prothrombin time ratio was calculated and acute traumatic coagulopathy defined as laboratory prothrombin time ratio >1.2. Transfusion requirements were recorded for the first 12 hrs following admission. Main Results:Three hundred patients were included in the study. Laboratory prothrombin time results were available at a median of 78 (62–103) mins. Point-of-care prothrombin time ratio had reduced agreement with laboratory prothrombin time ratio in patients with acute traumatic coagulopathy, with 29% false-negative results. In acute traumatic coagulopathy, the rotational thromboelastometry clot amplitude at 5 mins was diminished by 42%, and this persisted throughout clot maturation. Rotational thromboelastometry clotting time was not significantly prolonged. Clot amplitude at a 5-min threshold of ≤35 mm had a detection rate of 77% for acute traumatic coagulopathy with a false-positive rate of 13%. Patients with clot amplitude at 5 mins ≤35 mm were more likely to receive red cell (46% vs. 17%, p < .001) and plasma (37% vs. 11%, p < .001) transfusions. The clot amplitude at 5 mins could identify patients who would require massive transfusion (detection rate of 71%, vs. 43% for prothrombin time ratio >1.2, p < .001). Conclusions:In trauma hemorrhage, prothrombin time ratio is not rapidly available from the laboratory and point-of-care devices can be inaccurate. Acute traumatic coagulopathy is functionally characterized by a reduction in clot strength. With a threshold of clot amplitude at 5 mins of ≤35 mm, rotational thromboelastometry can identify acute traumatic coagulopathy at 5 mins and predict the need for massive transfusion.

The incidence and magnitude of fibrinolytic activation in trauma patients

Summary.  Background: Trauma is a global disease, with over 2.5 million deaths annually from hemorrhage and coagulopathy. Overt hyperfibrinolysis is rare in trauma, and is associated with massive fatal injuries. Paradoxically, clinical trials suggest a much broader indication for antifibrinolytics.

Activated Protein C Drives the Hyperfibrinolysis of Acute Traumatic Coagulopathy.

Background: Major trauma is a leading cause of morbidity and mortality worldwide with hemorrhage accounting for 40% of deaths. Acute traumatic coagulopathy exacerbates bleeding, but controversy remains over the degree to which inhibition of procoagulant pathways (anticoagulation), fibrinogen loss, and fibrinolysis drive the pathologic process. Through a combination of experimental study in a murine model of trauma hemorrhage and human observation, the authors’ objective was to determine the predominant pathophysiology of acute traumatic coagulopathy. Methods: First, a prospective cohort study of 300 trauma patients admitted to a single level 1 trauma center with blood samples collected on arrival was performed. Second, a murine model of acute traumatic coagulopathy with suppressed protein C activation via genetic mutation of thrombomodulin was used. In both studies, analysis for coagulation screen, activated protein C levels, and rotational thromboelastometry (ROTEM) was performed. Results: In patients with acute traumatic coagulopathy, the authors have demonstrated elevated activated protein C levels with profound fibrinolytic activity and early depletion of fibrinogen. Procoagulant pathways were only minimally inhibited with preservation of capacity to generate thrombin. Compared to factors V and VIII, proteases that do not undergo activated protein C–mediated cleavage were reduced but maintained within normal levels. In transgenic mice with reduced capacity to activate protein C, both fibrinolysis and fibrinogen depletion were significantly attenuated. Other recognized drivers of coagulopathy were associated with less significant perturbations of coagulation. Conclusions: Activated protein C–associated fibrinolysis and fibrinogenolysis, rather than inhibition of procoagulant pathways, predominate in acute traumatic coagulopathy. In combination, these findings suggest a central role for the protein C pathway in acute traumatic coagulopathy and provide new translational opportunities for management of major trauma hemorrhage.

Pre‐analytical heat treatment and a FVIII ELISA improve Factor VIII antibody detection in acquired haemophilia A

methods for assessment of b2M is needed. Unfortunately while an International Reference Material for b2M exists, it has not been universally utilized by all manufacturers for the b2M kits. Moreover, the initial ISS study, which involved 17 sites across three continents, did not report the method of b2M testing, and the methodology is unlikely to have been concordant across all institutions. Revalidation of the ISS for multiple myeloma with b2M and albumin results traceable to an international reference material may be necessary. The simplicity of the ISS makes it a highly desirable and practical scoring system. However, variances in the b2M assay performance may mean we are not providing our patients with consistent prognostic information across different centres. The last decade has seen considerable advances in myeloma treatment, including the addition of the novel agents, improvements in stem cell transplant techniques and better supportive care. It seems both appropriate and timely that we re-evaluate the prognostic information we give to our patients.

A computer-based model to assess costs associated with the use of factor VIII and factor IX one-stage and chromogenic activity assays.

Essentials Chromogenic factor VIII and factor IX assays have not been widely adopted partly due to perceived cost. Chromogenic assays may be needed for monitoring therapy with some extended half‐life concentrates. Efficient use of reagents makes the costs of chromogenic and one‐stage factor IX assays similar. A similar approach for factor VIII delivers lower costs for chromogenic compared with one‐stage assays.

The hemostatic properties of thawed pooled cryoprecipitate up to 72 hours

There is increasing interest in replacing fibrinogen early for the treatment of major hemorrhage. In countries where cryoprecipitate is the main concentrated source of fibrinogen, the thawing process complicates the timely availability of cryoprecipitate for transfusion early during major bleeding. The aim of the study was to investigate the hemostatic quality of cryoprecipitate, thawed and held at 18 to 24°C for up to 72 hours.

Diagnostic accuracy study of a factor VIII ELISA for detection of factor VIII antibodies in congenital and acquired haemophilia A

Antibody formation to factor VIII (FVIII) remains the greatest clinical and diagnostic challenge to the haemophilia-treating physician. Current guidance for testing for inhibitory FVIII antibodies (inhibitors) recommends the functional Nijmegen-Bethesda assay (NBA). A FVIII ELISA offers a complementary, immunological approach for FVIII antibody testing. It was the aim of this study to retrospectively evaluate the performance of a FVIII ELISA (index) for detection of FVIII antibodies, compared with the NBA (reference). All samples sent for routine FVIII antibody testing at two haemophilia Comprehensive Care Centres, were tested in parallel using the NBA and a solid-phase, indirect FVIII ELISA kit (Immucor). A total of 497 samples from 239 patients (severe haemophilia A=140, non-severe haemophilia A=85, acquired haemophilia A=14) were available for analysis. Sixty-three samples tested positive by the NBA (prevalence 12.7%, 95% confidence interval [CI], 9.9-15.9 %), with a median inhibitor titre of 1.2 BU/ml (range 0.7-978.0). The FVIII ELISA demonstrated a specificity of 94.0% (95%CI, 91.3-96.0), sensitivity of 77.8% (95%CI, 65.5-87.3), negative predictive value of 96.7% (95%CI, 94.5-98.2), positive predictive value 65.3% (95%CI, 53.5-76.0), negative likelihood ratio 0.2 (95%CI, 0.1-0.4), positive likelihood ratio 13.0 (95%CI, 8.7-19.3) and a diagnostic odds ratio of 54.9 (95%CI, 27.0-112.0). Strong positive correlation (r=0.77, p<0.001) was seen between the results of the NBA (log adjusted) and FVIII ELISA optical density. In conclusion, FVIII ELISA offers a simple, specific, surveillance method enabling batch testing of non-urgent samples for the presence of FVIII antibodies.

Evaluating the Use of a Negative D-Dimer and Modified Low Wells Score in Excluding above Knee Deep Venous Thrombosis in an Outpatient Population, Assessing Need for Diagnostic Ultrasound

Aims. Colour doppler ultrasonography (CDUS) is widely used in the diagnosis of deep venous thrombosis (DVT); however, the number of scans positive for above knee DVT is low. The present study evaluates the reliability of the D-dimer test combined with a clinical probability score (Wells score) in ruling out an above knee DVT and identifying patients who do not need a CDUS. Materials and Method. This study is a retrospective audit and reaudit of a total of 816 outpatients presenting with suspected lower limb DVT from March 2009 to March 2010 and from September 2011 to February 2012. Following the initial audit, a revised clinical diagnostic pathway was implemented. Results. In our initial audit, seven patients (4.9%) with a negative D-dimer and a low Wells score had a DVT. On review, all seven had a risk factor identified that was not included in the Wells score. No patient with negative D-dimer and low Wells score with no extra clinical risk factor had a DVT on CDUS (negative predictive value 100%). A reaudit confirmed adherence to our revised clinical diagnostic pathway. Conclusions. A negative D-dimer together with a low Wells score and no risk factors effectively excludes a lower limb DVT and an ultrasound is unnecessary in these patients.

A paired comparison of thawed and liquid plasma

To make plasma readily available to treat major hemorrhage, some centers are internationally using either thawed plasma (TP) or “never‐frozen” liquid plasma (LP). Despite the routine use of both, there are limited data comparing the two. The hemostatic properties of LP were evaluated and compared to TP in a paired study.

Effects of rivaroxaban on routine coagulation screening tests using commonly used reagents.

Direct oral anticoagulants (DOACs) have predictable pharmacokinetics and are licensed for stroke prevention in non-valvular atrial fibrillation (SPAF) and the treatment and secondary prevention of venous thromboembolism (VTE) without the need for monitoring. However there are occasions when it is useful to measure their effect and it is important that laboratories know the sensitivity of the screening reagents they use (Kitchen et al, 2014) when estimating the DOAC effect, as this may help with management (Baglin, 2013). Rivaroxaban concentrations can be calculated by measuring the anti-Xa effect of the drug in an assay calibrated using appropriate standards. Only 68 participants of the United Kingdom National External Quality Assessment Service (UKNEQAS) for Blood Coagulation external quality assurance scheme returned results for anti-Xa assays for rivaroxaban in September 2015, compared to 866 for prothrombin time (PT) and 889 for activated partial thromboplastin time (APTT) (UKNEQAS for Blood Coagulation, unpublished data), suggesting that these assays are not widely available. The effects of rivaroxaban on laboratory tests of haemostasis have been published, but most of the data are from spiking studies where drug is added to plasma/blood in vitro (Samama et al, 2010; Asmis et al, 2012), and some are from studies that measured ex vivo samples from healthy volunteers who have been given the drug (Asmis et al, 2012; Douxfils et al, 2013). The International Society on Thrombosis and Haemostasis (Baglin et al, 2013) and the British Committee for Standards in Haematology (Baglin et al, 2012) recommend that laboratories establish the sensitivity of screening reagents using commercially available calibrators, but this practice may underestimate drug concentration (Gosselin et al, 2015). In such studies, PT is considered to be more sensitive to rivaroxaban than APTT (Baglin, 2013). Innovin (Siemens Dade, Marburg, Germany) is the second most commonly used reagent by UKNEQAS participants, and appears to be insensitive to rivaroxaban when compared to other thromboplastins (Samama et al, 2010; Douxfils et al, 2013), emphasising the importance of studying the effect of rivaroxaban using local reagents. We therefore looked at the correlation between routine coagulation tests, using Innovin for PT and Siemens Actin FS (Siemens, Marburg, Germany) for APTT, and rivaroxaban concentrations in patients taking this DOAC for either SPAF or treatment/secondary prevention of VTE. A total of 124 consecutive plasma samples received in the laboratory between June 2012 and December 2015 from 91 patients taking rivaroxaban were frozen at 80°C and rapidly thawed at 37°C before analysis. All tests were performed on a Sysmex CS2100i coagulation analyser (Sysmex UK, Milton Keynes, UK). PT was measured in 123 samples and APTT was measured in 122 samples. Rivaroxaban concentration was measured using the BIOPHEN DiXal assay (Hyphen Biomed, Neuville-sur-Oise, France). Patients on rivaroxaban 10 mg od are predicted to have peak concentrations of 125 ng/ml (95% confidence interval [CI]: 91–195), and those on 20 mg od are predicted to have peak concentrations of 223 ng/ml (95%CI: 160–360) (Mueck et al, 2008) (Table I). In patients with rivaroxaban below 125 ng/ml, 65/67 (97%) had normal PT, 61/66 had normal APTT and 57/64 (89%) had normal PT and APTT. In patients with rivaroxaban below 223 ng/ml, 79/88 (90%) had normal PT, 73/87 (84%) had normal APTT, and 68/86 (79%) had normal PT