Laboratory Detection of the Antiphospholipid Syndrome via Calibrated Automated Thrombography

Lupus anticoagulants (LAC) consist of anti phospholipid antibodies, detected via their anti coagulant properties in vitro. Strong LAC relate to thromboembolic events, a hallmark of the anti-phospholipid syndrome. We have analyzed whether detection of this syndrome would benefit from thrombin generation measurements. Therefore, calibrated automated thrombography was done in normal plasma (n=30) and LAC patient plasma (n=48 non-anticoagulated, n=12 on oral anti coagulants), diluted 1: 1 with a normal plasma pool. The anti-beta(2)-glycoprotein I monoclonal antibody 23H9, with known LAC properties, delayed the lag time and reduced the peak height during thrombin generation induction in normal plasma dose-dependently (0-150 mu g/ml). At variance, LAC patient 1: 1 plasma mixtures manifested variable lag time prolongations and/or peak height reductions. Coupling these two most informative thrombin generation parameters in a peak height/lag time ratio,and upon normalization versus the normal plasma pool, this ratio distributed normally and was reduced in the plasma mixtures, for 59/60 known LAC plasmas. The normalized peak height/lag time ratio correlated well with the normalized dilute prothrombin time,diluted Russell's viper venom time and silica clotting time, measured in 1: 1 plasma mixtures (correlation coefficients 0.59-0.72). The anticoagulant effects of activated protein C (0-7.5 nM) or 23H9 (0-150 mu g/ml), spiked in the 1: 1 LAC plasma mixtures were reduced for the majority of patients, compatible with functional competition between patient LAC and activated protein C and LAC and 23H9, respectively. Hence,the normalized thrombin gene ration-derived peak height/lag time ratio identifies LAC in plasma with high sensitivity in a single assay, irrespective of the patient's treatment with oral anticoagulants

In vivo effects of contrast media on coronary thrombolysis

AbstractObjectives. The aim of the present study was to evaluate the influence of radiographic contrast media (CM) on alteplase-induced coronary thrombolysis.Background. Contrast media inhibit fibrinolysis in vitro and interact with endothelial cells, platelets and the coagulation system. The in vivo effects of CM on thrombolysis are not known.Methods. Occlusive coronary artery thrombosis was induced in 4 groups of 10 dogs by the copper coil technique. After 70 min of occlusion the dogs were randomized to intracoronary injection of 2 ml kg−1of either saline, a low-osmolar ionic CM (ioxaglate), a low-osmolar nonionic CM (iohexol) or a high-osmolar ionic CM (amidotrizoate). Thrombolysis with alteplase and co-therapy with aspirin and heparin was initiated after 90 min of occlusion. The coronary artery flow was monitored with an electromagnetic flowmeter throughout the experiment.Results. Iohexol and amidotrizoate, but not ioxaglate, were associated with longer reperfusion delays (time to optimal reperfusion: 67 ± 48 min and 65 ± 49 min, respectively, vs. 21 ± 11 min after placebo; p < 0.05) and shorter periods of coronary perfusion (optimal perfusion time: 21 ± 26 min and 21 ± 28 min, respectively, vs. 58 ± 40 min after placebo; p < 0.05). No significant differences were observed between groups with regard to activated partial thromboplastin times, circulating thrombin-antithrombin III complex concentrations and fibrinogen.Conclusions. In this animal model administration of iohexol and amidotrizoate before thrombolysis significantly delayed reperfusion. This interaction should be considered in the design of clinical trials of thrombolytic therapy that evaluate coronary artery patency and in patients receiving local infusions of fibrinolytic agents

Estimating the Cost-Effectiveness of Quality-Improving Interventions in Oral Anticoagulation Management within General Practice

AbstractObjectivesA clinical trial, “Belgian Improvement Study on Oral Anticoagulation Therapy (BISOAT),” significantly improved the quality after implementing four different quality-improving interventions in four randomly divided groups of general practitioners (GPs). The quality-improving interventions consisted of multifaceted education with or without feedback reports on their performance, international normalized ratio (INR) testing by the GP with a CoaguChek device or computer-assisted advice for adapting oral anticoagulation therapy. The quality improvement in INR control versus baseline was similar in the four groups. The aim of the current study was to calculate the cost-effectiveness and influencing factors of the four quality-improving interventions compared with usual care.MethodsActivity-based costing techniques with questionnaires were used to determine the global costs per patient per month in the different intervention groups. Effectiveness data were obtained from the BISOAT study. Cost-effectiveness was expressed as cost per additional day within a 0.5 range from INR target.ResultsThe one-time cost of multifaceted education was €49,997 for the whole study. Monthly continuous costs per intervention ranged between €37 and €54 per patient. Using the CoaguChek in combination with the multifaceted education was associated with net savings and quality improvement, hence dominated usual care. Sensitivity analyses showed improved cost-effectiveness with extended duration and with increased program size.ConclusionImplementation of the combination multifaceted education with the use of the CoaguChek is a cost-effective new organizational model of oral anticoagulation management in general practice

Lupus anticoagulant testing using plasma spiked with monoclonal antibodies: performance in the UKNEQAS proficiency testing programme

We report here results from a United Kingdom National Quality Assessment Scheme (UK NEQAS) exercise in which both plasma spiked with monoclonal antibodies and plasma from a patient known to have lupus anticoagulant (LA) were distributed to 245 hemostasis laboratories with a request for them to test for possible LA using their routine screening procedure. In general, good agreement was seen in the diagnosis of samples spiked with monoclonal antibodies against beta2-glycoprotein 1 (beta2GP1) and prothrombin, the LA-positive patient sample, and a normal pooled plasma; over 87% of centers correctly identified each sample. However, methods employing platelet neutralizing procedures were associated with a higher proportion of false-negative responses with the antiprothrombin-spiked sample, and it is important to recognize that sensitivity and responsiveness of different methods may vary between artificial plasmas and different LA-positive patient plasmas

A Higher Than Expected Incidence of Factor-viii Inhibitors in Multitransfused Hemophilia-a Patients Treated With An Intermediate Purity Pasteurized Factor-viii Concentrate

In May 1990, 218 patients with haemophilia A regularly attending the Leuven Haemophilia Center were randomly assigned to a group receiving either of two newly introduced factor VIII concentrates: factor VIII-P, an intermediate purity pasteurized concentrate, or factor VIII-SD, a high purity concentrate treated with solvent-detergent for viral inactivation. Patients were followed from May 1990 until October 1991. Between August 1991 and October 1991 a clinically important factor VIII inhibitor was detected in five out of the 109 patients receiving factor VIII-P while none of the 109 patients receiving factor VIII-SD developed such antibodies. All patients acquiring an inhibitor had previously been clinically tolerant to transfused factor VIII with 200 to more than 1,000 days of exposure to factor VIII prior to May 1990. Patients with inhibitors were transfused daily with 30 U factor VIII-SD per kg body weight, which was associated with a gradual decline of the inhibitor level. In all patients the antibodies were relatively slow-acting and predominantly directed towards the light chain of factor VIII. This study demonstrates a higher than expected incidence of factor VIII inhibitors associated with the use of a specific factor VIII concentrate in multitransfused haemophilia A patients. It indicates the usefulness of evaluating newly introduced concentrates in prospective, randomized trials

Anti-factor VIII antibodies of hemophiliac patients are frequently directed towards nonfunctional determinants and do not exhibit isotypic restriction.

A significant proportion of hemophilia A patients receiving transfusions of factor VIII (FVIII) develop a specific antibody response towards FVIII. These antibodies are usually detected by assays in which they inhibit the function of the molecule, such as the Bethesda clotting test. We have prepared anti-FVIII antibodies by specific immunoadsorption from the plasma of four hemophiliacs with stable inhibitor levels. The isotypic distribution of such antibodies was determined and their capacity to bind to insolubilized FVIII was compared with their inhibitory activity in two functional assays, namely, the Bethesda assay and a chromogenic assay. In addition, the FVIII epitope specificity was determined by competition with monoclonal antibodies for the binding to insolubilized FVIII. We show here that (1) anti-FVIII antibodies are not isotypically restricted; thus, a significant proportion of specific IgG2 was found; (2) antibodies are frequently directed towards epitopes of FVIII that are not directly involved in the function of the molecule and therefore escape detection in the Bethesda method or chromogenic assay; and (3) each patient shows a unique pattern of FVIII epitope recognition. We conclude that evaluation of anti-FVIII antibodies by a functional method does not provide an accurate evaluation of the specific antibody response. These findings have important implications for the comparison of the immunogenicity of FVIII molecules produced by different technologies and for the development of methods to control anti-FVIII antibody production