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ABSTRACT: Dabigatran etexilate is a new oral anticoagulant that functions as a direct thrombin inhibitor. An inhibitor of thrombin has the potential to interfere with essentially all clot-based coagulation assays and select chromogenic assays, whereas the drug would not be expected to interfere in antigen-based assays. The purpose of this study was to evaluate the effect of dabigatran on various specialized coagulation assays using normal plasma specimens with varying concentrations of dabigatran (the active form of dabigatran etexilate). We have demonstrated that samples containing therapeutic levels of dabigatran may lead to underestimation of intrinsic factor activities with abnormal activated partial thromboplastin time (aPTT) mixing study results and a false-positive factor VIII Bethesda titer; overestimation of protein C and protein S activity and activated protein C resistance ratio when determined using aPTT-based methods; and overestimation of results based on chromogenic anti-IIa assays but no effect on antigen assays and select chromogenic assays.
American Journal of Clinical Pathology 01/2013; 139(1):102-9. · 2.60 Impact Factor
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British Journal of Haematology 12/2012; · 4.94 Impact Factor
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British Journal of Haematology 09/2012; · 4.94 Impact Factor
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ABSTRACT: Low molecular weight heparins (LMWHs) are frequently used in the prophylaxis or treatment of venous thrombosis, acute coronary syndromes and peri-operative bridging. Major bleeding occurs in 1-4% depending on dose and underlying condition. Protamine is recommended for reversal but only partially reverses the anti-Xa activity and there are very limited data on clinical effectiveness. We retrospectively studied the effect of emergency reversal of LMWH with protamine in actively bleeding patients and patients requiring emergency surgery in our institution. Eighteen patients were identified through haematology referral/pharmacy records of protamine prescriptions between 1998 and 2009. Case notes were checked for the reversal indication, type/dose of LMWH, dose and clinical response to protamine, timing in relation to the last dose of LMWH and anti-Xa levels before and after protamine. All but one patient received enoxaparin. Fourteen were actively bleeding, three required emergency surgery without active bleeding and one had an accidental overdose without bleeding. The three patients requiring surgery had an uneventful procedure. In 12 of 14 patients with active bleeding, protamine could be evaluated. Bleeding stopped in eight. In the four with continuing bleeding, one had an additional coagulopathy. Protamine only partially affected anti-Xa levels. Protamine may be of use in reversing bleeding associated with LMWH but not in all patients. Anti-Xa levels were useful to assess the amount of anticoagulation before protamine administration but unhelpful in assessing its effect. Better reversal agents and methods to monitor LMWH therapy are required.
Blood coagulation & fibrinolysis: an international journal in haemostasis and thrombosis 10/2011; 22(7):565-70. · 1.25 Impact Factor
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ABSTRACT: Haemophilia A is caused by a reduction in clotting factor VIII (FVIII). FVIII coagulant activity (FVIII:C) can be measured by three methods; the one-stage activated partial thromboplastin time-based clotting assay, the two-stage Xa generation-based clotting assay and the chromogenic Xa generation-based assay. The FVIII:C of most patients with haemophilia A are concordant regardless of the assay method employed. Up to a third of patients show assay discrepancy, usually with the two-stage and chromogenic assays being much lower than the one-stage assay. Very rarely, patients have been reported with lower one-stage compared to two-stage and chromogenic assays, but here we report that the mutation p.Tyr365Cys accounts for most of these patients and, at least in the UK, is not rare. We have identified this mutation in 23 different families. Affected male index individuals had a lower mean one-stage FVIII:C of 27 iu/dl compared to two-stage FVIII:C mean of 77 iu/dl. Affected individuals had minimal or absent bleeding symptoms and when these were present they were usually in patients with another co-inherited bleeding disorder. Affected individuals often had surgery without the need to correct the one-stage FVIII:C.
British Journal of Haematology 09/2011; 154(5):618-25. · 4.94 Impact Factor
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British Journal of Haematology 06/2011; 154(3):311-24. · 4.94 Impact Factor
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ABSTRACT: Global hemostasis devices are currently being employed in operating rooms to assess the bleeding risk and outcomes for patients undergoing surgery. Two devices currently available are the TEG (Thromboelastograph; Haemoscope Corp., Niles, IL) and the ROTEM (Rotation Thromboelastometer; Pentapharm GmbH, Munich, Germany). Both measure the speed of clot formation, the strength of the clot when formed, and clot fibrinolysis kinetics. The two devices use different parameters so no cross comparisons of results can be made. The devices are usually operated by a member of the operating team and not a laboratory scientist; thus their testing and performance is generally not laboratory controlled, despite quality control being required to ensure reliable results. The UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation has undertaken a series of exercises evaluating the provision of External Quality Assessment (EQA) material for these devices. A series of four studies have taken place using lyophilized plasmas as the test material. Up to 18 TEG users and 10 ROTEM users have been involved in testing two samples per study, for a total of eight samples tested. The samples were normal plasmas, factor VIII or XI deficient samples, or normal plasmas spiked with heparin. The precision of the tests varied greatly for both devices, with coefficients of variances ranging from 7.1 to 39.9% for TEG and 7.0 to 83.6% for ROTEM. Some centers returned results that were sufficiently different from those obtained by other participants to predict alterations in patient management decisions. Our data indicate that regular EQA/proficiency testing is needed for these devices.
Seminars in Thrombosis and Hemostasis 10/2010; 36(7):757-63. · 4.52 Impact Factor
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ABSTRACT: Point-of-care testing (POCT) in haematology has seen a significant increase in both the spectrum of tests available and the number of tests performed annually. POCT is frequently undertaken with the belief that this will reduce the turnaround time for results and so improve patient care. The most obvious example of POCT in haemostasis is the out-of-hospital monitoring of the International Normalized Ratio in patients receiving a vitamin K antagonist, such as warfarin. Other areas include the use of the Activated Clotting Time to monitor anticoagulation for patients on cardio-pulmonary bypass, platelet function testing to identify patients with apparent aspirin or clopidogrel resistance and thrombelastography to guide blood product replacement during cardiac and hepatic surgery. In contrast to laboratory testing, POCT is frequently undertaken by untrained or semi-trained individuals and in many cases is not subject to the same strict quality control programmes that exist in the central laboratory. Although external quality assessment programmes do exist for some POCT assays these are still relatively few. The use of POCT in haematology, particularly in the field of haemostasis, is likely to expand and it is important that systems are in place to ensure that the generated results are accurate and precise.
British Journal of Haematology 09/2010; 150(5):501-14. · 4.94 Impact Factor
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ABSTRACT: We report the results of external quality assessment exercises in which 60 to 120 centers performed factor VIII (FVIII) inhibitor testing on a series of samples over a 13-year period. Samples from seven different subjects were distributed for analysis comprising the following: four different subjects with severe hemophilia A with antibodies following replacement therapy, one subject with acquired hemophilia A and antibodies to FVIII, one subject with normal FVIII and an easily detected lupus anticoagulant, and one subject with mild hemophilia A and a difficult-to-detect lupus anticoagulant but without antibodies to FVIII. In all of the surveys the results obtained in different centers analyzing the same sample varied to an extent that would influence patient management decisions. In the UK National External Quality Assessment Scheme surveys reported here, there was considerable interlaboratory variation in the results of FVIII inhibitor testing that did not improve over the survey period. The coefficient of variation of results in different centers was between 33% and 106% in samples from patients with severe congenital hemophilia A. In some cases, results were affected by assay components. For one plasma, the mean FVIII inhibitor results in centers using one source of normal plasma was 3.9 Bethesda unit (BU)/mL compared with a mean of 5.7 BU/mL in centers using a different normal plasma source ( P = 0.04). Our data indicate that the detection of FVIII inhibitors is not the same in different centers, and the degree of variability noted makes it likely that assay variability has contributed to the lack of international consensus in relation to the real incidence of FVIII inhibitors in different clinical settings. Improvements in assay standardization are urgently needed.
Seminars in Thrombosis and Hemostasis 11/2009; 35(8):778-85. · 4.52 Impact Factor
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Blood coagulation & fibrinolysis: an international journal in haemostasis and thrombosis 08/2009; 20(5):388-90. · 1.25 Impact Factor
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ABSTRACT: Global coagulation tests may have a better relation with phenotype in haemophilia than traditional coagulation tests. These include the Calibrated Automated Thrombin generation assay (CAT) and modified thromboelastometry using low tissue factor triggering. Both have shown marked variability in thrombin generation and clot formation profiles respectively despite similar FVIII:C levels and have been suggested as means to monitor treatment. Data with modified thromboelastometry are largely limited to severe and moderate haemophiliacs. CAT measurements in haemophilia are generally performed at low TF concentrations (1 pM) because of a higher sensitivity for the intrinsic pathway at this concentration but is also sensitive for FVIII at higher concentrations (5 pM) and this has the advantage that inhibition of contact factor activation can be avoided. No formal comparison of both TF concentrations has been reported and the data on modified thromboelastometry in mild haemophilia are limited.
In this study we compared thrombin generation at 1 and 5 pM in 57 haemophilia patients without exposure to treatment and 41 patients after treatment. We also assessed the sensitivity of thromboelastometry for haemophilia A in 29 patients.
We found that CAT discriminates well between normal individuals and haemophilia patients; also FVIII:C correlates well with the ETP/peak. We found no clear advantages of measurements at 1 compared to 5 pM but found increased variation over time at 1 pM. The sensitivity of modified thromboelastometry for haemophilia A was less than CAT with abnormal measurements largely limited to severe and moderate patients. Larger studies correlating both methods with clinical outcome are required.
Thrombosis Research 12/2008; 123(6):895-901. · 2.44 Impact Factor
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ABSTRACT: Point-of-care (POC) testing in the field of hemostasis is rapidly expanding in many countries. This includes use of global tests of hemostasis in operating theaters and especially use of POC monitors for determination of the international normalized ratio (INR) for monitoring oral anticoagulant therapy. Issues related to internal quality control and external quality assessment for these devices are reviewed. Data from external quality assessment exercises involving users of several different POC-INR devices is described, and use of split samples where a patient sample is analyzed by both a POC device and by a conventional laboratory method is described.
Seminars in Thrombosis and Hemostasis 11/2008; 34(7):647-53. · 4.52 Impact Factor
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ABSTRACT: Even though new anticoagulants are being devised with the notion that they do not require regular monitoring, when bleeding occurs, it is important to have an antidote and a reliable test to confirm whether the anticoagulant effects are persisting. We examined the effects of five heparinoids, unfractionated heparin (UFH), tinzaparin, enoxaparin, danaparoid and fondaparinux on the traditional APTT and anti-Xa assays as well as on the calibrated automated thrombogram (CAT). We also studied the ability of protamine sulphate (PS), NovoSeven, FEIBA and FFP to reverse maximum anticoagulation induced by the different heparinoids. The CAT was the only test to detect the coagulopathy of all the anticoagulants. PS produced complete reversal of UFH, and this could be monitored with all three tests. Tinzaparin can also be completely neutralised in vitro with high doses of PS, but the maximum enoxaparin reversal achieved with PS is only approximately 60%. Fondaparinux does not significantly affect the APTT and PS has no significant effect on its reversal. Only NovoSeven was able to correct the fondaparinux induced CAT abnormalities whilst having no effect on the anti-Xa level. None of the reversal agents was very effective in danaparoid spiked plasma but NovoSeven, at high dose, increased the ETP by 40% and reduced the anti-Xa level from 0.93 to 0.78 IU/ml. We conclude that the CAT is superior to the traditional coagulation tests in that it not only detects the coagulopathy of all the heparinoids but can be also be used to monitor their reversal.
Thrombosis and Haemostasis 09/2008; 100(2):350-5. · 5.04 Impact Factor
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American Journal of Clinical Pathology 06/2008; 129(5):825-6. · 2.60 Impact Factor
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ABSTRACT: Accurate and precise measurement of plasma D-dimer levels is important in the diagnosis and management of venous thromboembolism. Considerable variability in D-dimer results obtained using different methods has, however, been reported in multicentre studies. This study explored in two separate multicentre exercises the degree of precision amongst laboratory D-dimer measurements, and the degree by which inter-method agreement could be improved using a calibration curve model. The first exercise demonstrated generally good within-centre precision, with 82% of the centres reporting results for two identical but differently coded samples within 10% of each other. However, six centres reported results which would have excluded deep vein thrombosis (DVT) for one sample but failed to exclude DVT for the other, identical sample. In the second exercise, overall between-method precision of D-dimer results for two samples was shown to improve markedly when a calibration model was applied, using the consensus median values obtained by all participants for three "calibration plasmas" to recalculate D-dimer values. For centres reporting results in fibrinogen equivalent units (FEUs), between-centre coefficients of variation (CVs) fell from 25.9% to 11.6% and 22.4% to 7.7%, respectively, for the two samples. For centres reporting in ng/ml, CVs fell from 45.3-21.6% and 40.8-11.6%, respectively. In conclusion, improved harmonisation of D-dimer results by different methods may be achieved by a calibration model and common calibrant plasmas.
Thrombosis and Haemostasis 12/2007; 98(5):1127-35. · 5.04 Impact Factor
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11/2007: pages 8 - 17; , ISBN: 9780470988633
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Thrombosis and Haemostasis 10/2007; 98(3):691-2. · 5.04 Impact Factor
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Clinical Chemistry 09/2007; 53(8):1555-6; author reply 1556-7. · 7.91 Impact Factor
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ABSTRACT: The new CoaguChek XS system is designed for use in patient selftesting. It is the successor of the current CoaguChek S system. The detection principle is based on the amperometric measurement of the thrombin activity initiated by starting the coagulation cascade using a human recombinant thromboplastin. This study was performed to assign the International SEnsitivity Index (ISI) to the new test according to the WHO guidelines for thromboplastins and plasmas used to control anticoagulant therapy, and to establish the measuring range of the new system. At four study sites a total of 90 samples of normal donors and 291 samples of warfarin-, phenprocoumon- or acenocoumarol-treated patients were included in the study. The ISI value of the new test was assigned against the human recombinant reference thromboplastin rTF/95 at each site using the samples from stabilized patients in the International Normalized Ratio (INR) range between 1.5 and 4.5 only. The new point-of-care system's measuring range between 0.8 and 8 INR was calibrated against the mean INR of rTF/95 and AD149 using polynomial regression. ISIs were (CV of the slope): Site 1: ISI 0.99 (1.1%); Site 2: ISI 1.02 (2.0%); Site 3: ISI 1.03 (1.1%); Site 4: ISI 1.00 (1.4%). All regression lines calculated from patient-only data pass through the normal donor data points. All CVs of the slopes of the orthogonal regression lines are well below 3%, thus fulfilling the requirements of the WHO guidelines. The mean ISI for the new CoaguChek XS PT Test is 1.01.
Thrombosis and Haemostasis 06/2007; 97(5):856-61. · 5.04 Impact Factor
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ABSTRACT: The consequences of an erroneous thrombophilia diagnosis may be serious if it is used to determine clinical management. Therefore careful selection, assessment, and control of laboratory tests for thrombophilia are essential. As for other coagulation tests, the pre-analytical phase must be carefully controlled with attention to the specific problems associated with each type of assay. The investigator must then recognize that for most laboratory tests of thrombophilia, there are a number of assay types available, often based on different principles of analysis. This creates the potential for different users to obtain varying results depending on the technique employed. Such problems can occur in assays of antithrombin activity, depending on whether the assay employs factor Xa, human thrombin, or bovine thrombin. In clot-based assays of protein C and protein S, there can be specificity problems related to interference by factor V Leiden (FVL), antiphospholipid antibodies, and other substances. Even genetic tests can give erroneous results and should not automatically be seen as absolute without supporting evidence and careful quality-control measures. Whatever technique is selected, it is mandatory to incorporate sufficient concurrent quality-control samples to validate the results of thrombophilia tests. These should include assessment of the parameter at normal and abnormal levels to give confidence in results across the measurement range that would normally be encountered in routine practice. This should be used in conjunction with regular participation in external quality assessment (EQA) (which has been linked to improved laboratory performance in thrombophilia testing). Larger EQA programs can provide information concerning the relative performance of analytical procedures, including the method principle, reagents, and instruments. Herein, we describe many of the methodologic effects in detail. We use specific examples to illustrate the general principle that, in performing laboratory testing for thrombophilia, one must always consider the performance characteristics and limitations of the assay in use.
Seminars in Hematology 05/2007; 44(2):114-25. · 3.99 Impact Factor
