Lennart Stigendal

Effects of the oral, direct factor Xa inhibitor rivaroxaban on commonly used coagulation assays.

Summary.  Introduction: Rivaroxaban is an oral direct factor Xa inhibitor developed for prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary but the dose‐dependent effects on common reagents and assay procedures are largely unknown. Objectives: To investigate the effect of rivaroxaban on commonly used coagulation assays. Materials and Methods: Rivaroxaban was added to plasma from healthy subjects in the concentration range 0–1000 μg L−1 and analyzed using different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, fibrinogen and activated protein C (APC) resistance assays. Results: At an expected peak concentration of rivaroxaban in clinical use, the APTTs were almost invariably prolonged but at lower concentrations the effect was weak. The concentration needed to double the APTT varied between 389 ± 106 and 617 ± 149 μg L−1 for different reagents. The PT assays showed a marked degree of difference. In general, the Quick PT type assays were more sensitive compared with the Owren type PT assays. The results from antithrombin assays were dependent on the type of reagent, with the Xa‐based assay being sensitive for rivaroxaban with an estimated increase of 0.09 IU mL−1 per 100 μg L−1 rivaroxaban. There were only minor effects on fibrinogen assays based on thrombin reagents. The APTT‐based assay for APC resistance is affected in a dose‐dependent manner whereas an assay based on the activation of coagulation at the prothrombinase level was unaffected. Conclusions: Different assays, and even different reagents within an assay group, display variable effects by therapeutic concentrations of rivaroxaban.

Experimental exposure to wood-smoke particles in healthy humans : Effects on markers of inflammation, coagulation, and lipid peroxidation

Particulate air pollution is known to increase cardiovascular morbidity and mortality. Proposed mechanisms underlying this increase include effects on inflammation, coagulation factors, and oxidative stress, which could increase the risk of coronary events and atherosclerosis. The aim of this study was to examine whether short-term exposure to wood smoke affects markers of inflammation, blood hemostasis, and lipid peroxidation in healthy humans. Thirteen subjects were exposed to wood smoke and clean air in a chamber during two 4-h sessions, 1 wk apart. The mass concentrations of fine particles at wood smoke exposure were 240–280 μg/m3, and number concentrations were 95,000–180,000/cm3. About half of the particles were ultrafine (< 100 nm). Blood and urine samples were taken before and after the experiment. Exposure to wood smoke increased the levels of serum amyloid A, a cardiovascular risk factor, as well as factor VIII in plasma and the factor VIII/von Willebrand factor ratio, indicating a slight effect on the balance of coagulation factors. Moreover, there was an increased urinary excretion of free 8-iso-prostaglandin2α, a major F2-isoprostane, though this was based on nine subjects only, indicating a temporary increase in free radical-mediated lipid peroxidation. Thus, wood-smoke particles at levels that can be found in smoky indoor environments seem to affect inflammation, coagulation, and possibly lipid peroxidation. These factors may be involved in the mechanisms whereby particulate air pollution affects cardiovascular morbidity and mortality. The exposure setup could be used to establish which particle characteristics are critical for the effects.

Effects of the oral, direct thrombin inhibitor dabigatran on five common coagulation assays

Dabigatran is an oral, reversible thrombin inhibitor that has shown promising results in large clinical trials. Laboratory monitoring is not needed but the effects on common coagulation assays are incompletely known. Dabigatran was added to plasma from healthy subjects in the concentration range 0-1,000 μg/l and analysed using several reagents for activated thromboplastin time (APTT), prothrombin time (PT), fibrinogen, antithrombin, and activated protein C resistance. Typical trough concentrations are about 50 μg/l, peak concentrations 100-300 μg/l. At 100 μg/l all APTT-results were prolonged. The concentration required to double APTT ranged between 227 and 286 μg/l, the responses for all five reagents were similar. PT-reagents were much less affected with almost no samples above INR 1.2 at 100 μg/l. The effect was sample dilution dependent with PT Quick type more sensitive than PT Owren type methods. If a patient on dabigatran has prolonged APTT, >90 seconds, and Quick PT INR>2 or Owren PT INR>1.5 over-dosing or accumulation of dabigatran should be considered. Two of four fibrinogen reagents underestimated the fibrinogen concentration considerably at expected peak concentration. Methods based on inhibition of thrombin over-estimated the antithrombin concentration, but not Xa-based. The APC-resistance methods over-estimated the APC-ratio, which may lead to miss-classification of factor V Leiden patients as being normal. Different coagulation assays, and even different reagents within an assay group, display variable effects at therapeutic concentrations of dabigatran. Some of these assay variations are of clinical importance, thus knowledge is needed for a correct interpretation of results.

GUIDELINES ON PREPARATION, CERTIFICATION, AND USE OF CERTIFIED PLASMAS FOR ISI CALIBRATION AND INR DETERMINATION

See also van den Besselaar AMHP, Barrowcliffe TW, Houbouyan-Re veillard LL, Jespersen J, Johnston M, Poller L, Tripodi A on behalf of the Subcommittee on Control of Anticoagulation of the Scientific and Standardization Committee of the ISTH. Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination. J Thromb Haemost 2005; 2: 1946–53; van den Besselaar AMHP. Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination – reply to a rebuttal. This issue, pp 2371–2.

Incidence of symptoms and AIDS in 146 Swedish haemophiliacs and blood transfusion recipients infected with human immunodeficiency virus.

The times from infection with the human immuno-deficiency virus (HIV) to the onset of the first clinical symptom and the development of AIDS were studied prospectively in 98 haemophiliacs and 48 blood transfusion recipients infected with the virus. Patients were followed up for a median of 61 months after infection, the dates of infection being either known exactly or estimated from the interval between the last negative and first positive HIV antibody test result. The rate of progression to AIDS was significantly higher for the transfusion recipients than for the haemophiliacs. The difference in time to the occurrence of the first clinical symptom was less pronounced between the two groups, though pointing in the same direction. The results suggest that on average roughly half of all patients positive for HIV will develop some clinical sign or symptom within five to six years after infection.

Risk of clinically relevant bleeding in warfarin‐treated patients—influence of SSRI treatment

To investigate the risk of clinically relevant bleeding in warfarin‐treated patients with or without concomitant treatment with selective serotonin reuptake inhibitors (SSRIs).

Local INR calibration of the Owren type prothrombin assay greatly improves the intra- and interlaboratory variation A three-year follow-up from the Swedish national external quality assessment scheme

In 1999, a simplified procedure for calibration of the Owren prothrombin time (Owren PT) assay was introduced by a working group of the organisation for national quality assurance in laboratory medicine in Sweden. The new protocol allowed local calibration by means of only two lyophilised national plasma calibrators and expression of results as an international normalized ratio (INR). This is our report of a three-year follow-up involving the analysis of data from all laboratories, in hospitals (n=88 in 2002) and primary health care units (n=246 in 2002) that perform the Owren PT assay in Sweden. The interlaboratory variation was significantly improved after the introduction of the new calibration procedure. For the larger hospital-based laboratories, the mean coefficient of variation (CV) was reduced from 7.9% to 5.2% (p<0.0001) when analysing test materials with INR range 2-4. In the higher INR range (>4), the CV was reduced even further, from 10.4% to 6.8% (p<0.0001). The corresponding results from smaller laboratories in the primary health care units showed a similar decrease in CV from 8.2% to 5.7% in the INR range 2-4 (p<0.0001). At the INR range >4, the CV was reduced from 9.5% to 7.8%. The intralaboratory variation was also improved for both types of laboratory categories. This study shows an improved precision, with CV less than 6% at the therapeutic INR range, for both hospital-based laboratories and smaller laboratories in the primary health care system. The results indicate that the Owren PT assay is well suited for local INR calibration employing only two calibrant plasmas in a simplified procedure.

An instrument for measuring health-related quality of life in patients with Deep Venous Thrombosis (DVT): development and validation of Deep Venous Thrombosis Quality of Life (DVTQOL) questionnaire

BackgroundFew studies have evaluated patient-reported outcomes in connection with a primary event of deep venous thrombosis, partly due to a lack of disease-specific measures. The aim here was to develop a disease-specific health-related quality of life (HRQL) measure, the deep venous thrombosis quality of life questionnaire (DVTQOL), for patients with recent exposition and treatment of proximal deep venous thrombosis.MethodsA total of 121 consecutive outpatients (50 % males; mean age 61.2 ± 14 years) treated with warfarin (Waran®) for symptomatic proximal deep venous thrombosis were included in the study. Patients completed the SF-36, EQ-5D and the pilot version of the DVTQOL.ResultsItems having: high ceiling and floor effect, items with lower factor loadings than 0.50 and items loading in several factors were removed from the pilot version of DVTQOL. In addition, overlapping and redundant items identified by the Rasch analysis were excluded. The final DVTQOL questionnaire consists of 29 items composing six dimensions depicting problems with: emotional distress; symptoms (e.g. pain, swollen ankles, cramp, bruising); limitation in physical activity; hassle with coagulation monitoring; sleep disturbance; and dietary problems. The internal consistency reliability was high (alpha value ranged from 0.79 to 0.93). The relevant domains of the SF-36 and EQ-5D significantly correlated with DVTQOL, thereby confirming its construct validity.ConclusionsThe DVTQOL is a short and user-friendly instrument with good reliability and validity. Its test-retest reliability and responsiveness to change in clinical trials, however, must be explored.

Home Treatment of Deep Vein Thrombosis An Out-Patient Treatment Model with Once-Daily Injection of Low-Molecular-Weight Heparin (Tinzaparin) in 555 Patients

During a 22-month period, 555 consecutive patients at seven hospitals in the western part of Sweden with an acute deep vein thrombosis (DVT) not involving the iliac vein and not having pulmonary embolism were included in a study testing the efficacy of implementing out-patient treatment. For all patients with a confirmed diagnosis of acute DVT, a folder was used that contained two checklists with detailed instructions for further treatment, one for the doctor and one for the nurse, an information pamphlet for the patient and prepared prescriptions for low-molecular-weight heparin (LMWH) tinzaparin (Innohep®) of 175 anti-Xa IU/kg body weight subcutaneously once daily and warfarin. Patients not requiring hospitalisation, according to strict guidelines, were then eligible for treatment as out-patients. Prior to release from the emergency department for home treatment, a nurse provided detailed information to the patient and administered the first tinzaparin injection. In 194 (35.0%) out of 555 patients, the DVT was localised only in the lower leg not reaching the popliteal vein. Factors predisposing to venous thromboembolism were identified in 35.0% of the patients. 332 (59.8%) out of the 555 patients studied did not require hospitalisation and were therefore treated as out-patients. 140 of these patients (42.2%) injected themselves, the injection was given by a relative in 63 (19.0%) patients and by the community nurse in 129 (38.9%). Six (1.8%) patients reported a worsening of the DVT condition during the LMWH treatment period. No major bleedings were observed during the injection treatment period. Except for local minor skin bleedings at the injection site, only 3 (0.9%) patients reported minor bleedings during the injection treatment period. Recurrences of venous thromboembolism during the first 2 months were reported in 9 patients (2.7%) out of 332 patients who were sent home from the emergency department. Five (2.2%) patients out of the 223 who were admitted to the hospital had an increased tendency to bleeding. Twelve patients (5.4%) were hospitalised because of a pronounced local status, 26 (11.7%) were senile, social factors were the reason for hospitalisation in 76 (34.1%) and lack of time of the physician in 39 (17.5%) of the patients. A pharmacoeconomic analysis found a cost reduction of 69% with the present model for home treatment compared with traditional in-hospital treatment of DVT patients. We conclude that tinzaparin can be safely used at home by patients with DVT below the inguinal region and that the model used in the present study is cost-effective.

NovoSeven in warfarin-treated patients

&NA; Haemorrhages represent a major complication of treatment with vitamin K antagonists. In cases of severe bleeding, a prompt effect on the increased International Normalized Ratio value is vital to achieve haemostasis. As conventional treatment, that is plasma or plasmaderived concentrates, carries the risk of blood‐borne virus transmission, new treatments are needed. An open, multicentre pilot trial is currently under way to determine the effect of recombinant activated factor VII (rFVIIa; NovoSeven®) administered to patients experiencing a bleeding episode after receiving vitamin K antagonists. When rFVIIa was given to a patient with a warfarin‐induced nosebleed, it had an immediate haemostatic effect and the International Normalized Ratio value virtually normalized. Blood Coagul Fibrinolysis 11 (suppl 1):S113‐S115