thromboplastin and coumarin

From injury through healing, thrombin has several important functions in blood clotting, subsequent clot lysis, and tissue repair. These include edema, inflammation, cell recruitment, cellular releases, transformations, mitogenesis, and angiogenesis. Thrombin also participates in disease states, such as venous thrombosis, coronary thrombosis, stroke, and pulmonary emboli, among others and is implicated in atherosclerosis, the growth and metastasis of certain cancers, Alzheimer's disease, and perhaps other conditions. Thrombin must be continually generated to sustain normal and pathogenic processes. This is because of a variety of consumptive mechanisms. Unlike other activated factors in thrombotic and fibrinolytic pathways, and because thrombin promotes its own generation (feedback and cellular activation), thrombin is a primary target for therapeutics. Besides recombinant hirudins, Argatroban (Novastan) and Bivalirudin (Hirulog) are promising thrombin-directed inhibitors for antithrombotic intervention.

Topics: Blood Coagulation; Blood Coagulation Factors; Coumarins; Enzyme Activation; Factor VIII; Fibrinolytic Agents; Heparin; Hirudins; Humans; Prothrombin; Thrombin; Thromboplastin; Vitamin K

To simplify International Sensitivity Index (ISI) calibration, the possibility of substituting fresh plasma for fresh whole-blood samples with point-of-care testing (POCT) whole-blood monitors was investigated in a three-center study of three different POCT systems.. A modified full WHO calibration procedure based on 20 healthy controls and 60 coumarin-treated patients was performed on three monitoring systems with whole-blood and plasma samples against plasma tested using the European Concerted Action on Anticoagulation (ECAA) rabbit reference plain thromboplastin and the manual prothrombin time (PT) method.. With one of the three systems, the mean ISI was 1.51 for whole blood and 1.49 for plasma; with the second system, the mean ISI was 1.08 for both whole blood and plasma. With the third system, however, the difference between the mean ISI for whole blood and that for plasma was greater (1.15 and 1.01, respectively). Overall, the precision of the calibrations was less than with traditional manual plasma PT testing.. Provided that an appropriate calcium chloride concentration is used, the plasma PT results can be used for accurate ISI calibration of two of these three whole-blood POCT systems. Precision criteria need to be modified for POCT monitors.

Topics: Administration, Oral; Animals; Anticoagulants; Calibration; Coumarins; Europe; Humans; International Cooperation; International Normalized Ratio; Plasma; Point-of-Care Systems; Prothrombin Time; Rabbits; Reference Standards; Reference Values; Thromboplastin

An alternative approach to INR estimation is for laboratories to calibrate their own local system using calibrant plasmas supplied by manufacturers or reference laboratories. The purpose of the present study was to investigate the within-laboratory variability of a calibrant plasma procedure using various sets of lyophilized plasmas. INR had been assigned to 13 calibrant plasmas in a previous multi-center study. Each of 10 other ("field") laboratories measured PTs in the 13 calibrant plasmas and in 15 local fresh coumarin plasmas, using three different thromboplastin reagents. Each fresh coumarin PT was converted to INR using a calibration procedure with a set of 4 calibrants (1 normal + 3 abnormals). The abnormals of each set were either coumarin or artificial and were used with different assigned INR. When the INR had been assigned with a thromboplastin brand identical to the thromboplastin in the field laboratory, the procedure was named "reagent-specific" calibration. Otherwise the procedure was named "dissimilar" calibration. Using "reagent-specific" calibration procedures, relatively homogeneous INR were obtained for the fresh coumarin plasmas, whatever type of calibrant was used. In contrast, discrepant INR were obtained when "dissimilar" cross-species calibration procedures were used. The study was limited to 9 laboratories using the same type of coagulometer and one using a different type.

Topics: Anticoagulants; Blood Coagulation; Calibration; Coumarins; France; Freeze Drying; Humans; Indicators and Reagents; International Normalized Ratio; Laboratories; Netherlands; Plasma; Prothrombin Time; Recombinant Proteins; Reference Standards; Reproducibility of Results; Sample Size; Thromboplastin

The 'high and low responder phenomenon' of monocyte tissue factor (MTF) activity has been attributed to effects on monocytes by granulocytes, platelets and lipopolysaccharide (LPS). To study the possible contribution of plasma to the high and low responder phenomenon, we measured the MTF activity in isolated cryopreserved human monocytes from two donors (monocytes A and monocytes B) after incubation in a plasma environment depleted of granulocytes, platelets and LPS. In buffer only, MTF activity was 643 and 679 fM (fM = final concentration of tissue factor), in normal pooled plasma, it was 1478 and 1615 fM (P = 0.001), respectively, in monocytes A and in monocytes B. Incubation with individual plasma samples from healthy controls (n = 43) gave a median MTF of 1355 fM (range 1044-1976 fM) and 1329 fM (range 858-1951 fM) respectively. A plasma consistently induced a higher or lower level of MTF activity in both monocytes: r = 0.82 (P < 0.00001). Coumarin use did not influence the high and low responder phenomenon. In the absence of granulocytes, platelets and LPS, plasma determines the high and low responder phenomenon. This phenomenon is not influenced by coumarin treatment.

Topics: Aged; Anticoagulants; Arthroplasty, Replacement, Hip; Blood Coagulation; Case-Control Studies; Cell Culture Techniques; Cells, Cultured; Coumarins; Cryopreservation; Culture Media, Serum-Free; Female; Hip Fractures; Humans; International Normalized Ratio; Leukocytes, Mononuclear; Male; Middle Aged; Plasma; Postoperative Complications; Statistics, Nonparametric; Thromboplastin

For determination of the international normalized ratio (INR), it has been suggested that "highly sensitive" thromboplastin reagents (International Sensitivity Index [ISI] < or = 1.2) provide the most consistent performance and minimize interlaboratory variability. We compared the INR values obtained from 69 specimens drawn from patients receiving long-term oral anticoagulant therapy, using four thromboplastin preparations (manufacturer-assigned ISI range of 0.96-1.10) and two automated photo-optical analyzers. Multivariate analysis of the INR response matrix (552 INR values) indicated that the eight reagent-coagulometer combinations did not produce equivalent INR values. Similar analysis indicated that INR values were not normalized when uncorrected prothrombin ratios or INR values, calculated after assignment of "local ISI values" to each thromboplastin reagent, were compared. The INR differences also seemed to be clinically significant because 17% to 29% of paired thromboplastin values were discordant when all INR values were assigned to one of four therapeutic categories used in oral anticoagulant therapy (< 2.0; 2.0-3.0; 3.0-4.5; or > 4.5). These differences in INR values obtained with two photo-optical coagulometers and four highly sensitive thromboplastin reagents suggest that the existing INR system has not achieved the goal of standardized prothrombin time values and does not support the recommendation to use only highly sensitive reagents for the regulation of oral anticoagulant therapy.

Topics: Anticoagulants; Coumarins; Humans; Indicators and Reagents; Multivariate Analysis; Prothrombin Time; Reference Values; Regression Analysis; Sensitivity and Specificity; Thromboplastin

A new PT reagent based on recombinant human tissue factor and synthetic phospholipids (phosphatidyl choline and phosphatidyl serine) with defined fatty acid side chains was calibrated against BCT/253 and CRM 149R. A small but consistent bias in the International Sensitivity Index (ISI) value was obtained using either the human or rabbit brain reference material. ISI values were around 1.0 or slightly lower depending on the respective instrument. Mixing studies with factor deficient plasmas showed a high factor sensitivity especially for factor VII as compared to commercial rabbit brain or human placenta thromboplastin. In an international field trial the reagent was tested using fully or semi automated Electra coagulometers in 4 different laboratories. Results with normal samples were in excellent agreement among the different laboratories. Mean values were 10.9, 10.9, 11.0, 11.2 s with a range of 9.5 to 12.5 s. Results of males and females were not different. In patients with liver disease very similar PT activities were found as compared to sensitive rabbit brain or human placental thromboplastins. In normals and patients with oral anticoagulation INR values correlated very well against BCT (r = 0.98, regression line y = -0.07 + 0.9 x). The distribution of samples was linear over the whole range. In the comparison against sensitive rabbit brain thromboplastin or human placental thromboplastin similar correlations were found. In a few cases higher INR values were observed for the recombinant reagent especially in patients with intensive treatment. Factor assays in those patients showed at least the strong reduction of one vitamin K-dependent coagulation factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Brain Chemistry; Calibration; Coumarins; Evaluation Studies as Topic; Female; Heparin; Humans; Indicators and Reagents; Liver Diseases; Male; Phospholipids; Placenta; Pregnancy; Prothrombin Time; Rabbits; Recombinant Proteins; Reference Standards; Thromboplastin

The International Sensitivity Index (ISI) for different thromboplastin reagents is obtained by calibration against WHO reference preparations. It is hoped that calculation of the International Normalized Ratio (INR) from the ISI will permit accuracy and conformity in reporting laboratory assays of warfarin effect even across a range of different techniques. We have examined the INR values of 128 warfarin patients obtained by four different techniques in common use, namely venous and capillary Thrombotest and venous and capillary Manchester reagent. Discrepant INR values were obtained. The mean Manchester venous INR values were lower than those obtained by the other three methods (P less than 0.0001). This suggests that patients dosed by reference to Manchester venous INR are liable to receive more warfarin than those dosed by the other methods.

Topics: Animals; Blood Coagulation Tests; Brain Chemistry; Capillaries; Coumarins; False Negative Reactions; Humans; Rabbits; Reagent Kits, Diagnostic; Reference Standards; Thromboplastin; Thrombosis; Veins; Warfarin

Topics: Coumarins; Drug Tolerance; Heparin; Humans; Immune Tolerance; Plasma; Thromboplastin

Topics: Anticoagulants; Coumarins; Factor XI; Humans; Liver Cirrhosis; Liver Cirrhosis, Alcoholic; Thromboplastin

Topics: Anticoagulants; Coumarins; Humans; Thromboplastin

Topics: Anticoagulants; Coumarins; Humans; Thromboplastin

Topics: Antifibrinolytic Agents; Coumarins; Humans; Thromboplastin; Vitamin K; Vitamin K 1

Topics: Anticoagulants; Coumarins; Humans; Jaundice; Prothrombin; Prothrombin Time; Thromboplastin

Topics: Blood Coagulation; Coumarins; Dicumarol; Eating; Thromboplastin

Topics: 4-Hydroxycoumarins; Animals; Blood Coagulation; Brain; Coumarins; Dicumarol; Rabbits; Thromboplastin