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Biomedical subjects

A Tripodi

Publications and source records attributed to A Tripodi.

At least 91 records · Page 5Linked to original sources
PubMed1996

Markers of activated coagulation and their usefulness in the clinical laboratory.

Currently, information on hypercoagulability can be achieved directly--through measuring the enzymatic forms of coagulation zymogens generated during coagulation activation--or indirectly--through measuring the activation peptides generated when zymogens are activated or the enzyme-inhibitor complexes formed by inhibition of the enzymes by their plasmatic inhibitors. On the basis of published results, markers of activated coagulation are considered useful for investigating mechanisms that regulate hemostasis. They can also be used to better characterize patients at increased thrombotic risk. However, they should be considered indices of hypercoagulability, not of the risk of thrombosis, until prospective studies can demonstrate that alterations of these markers can predict the occurrence of thrombosis. For diagnosing acute thrombosis, their usefulness is questionable; they are less effective than markers of fibrinolysis activation such as the D-dimer. Finally, their use to monitor anticoagulant treatment is still premature and needs investigation in well-designed clinical studies.

Anticoagulants↗
PubMed1996

A simplified procedure for thromboplastin calibration--the usefulness of lyophilized plasmas assessed in a collaborative study.

The International Sensitivity Index (ISI) of thromboplastins is determined by calibration using fresh plasmas from 60 patients stabilized on oral anticoagulants and 20 healthy subjects. This procedure is demanding, particularly for those who have no easy access to patients. The alternative use of a smaller number of lyophilized plasmas has already been considered, but one important issue, the number of repeated measurements to be carried out, has never been addressed. Two commercial rabbit thromboplastins, A and B, were calibrated in 3 laboratories against CRM 149R. On each of 10 working days, prothrombin times were measured for a different set of 8 fresh plasmas and for the same set of 8 lyophilized plasmas. The ISI values for both thromboplastins were estimated by orthogonal regression on fresh and lyophilized plasmas. The between- and within-laboratory CV values of the estimated ISI were taken as measures of precision of the calibration. In addition, ISI and CV were calculated daily on cumulative results obtained with lyophilized plasmas from day 1 to day 10. The ISI values for both thromboplastins calculated with lyophilized plasmas were not significantly different from those with fresh plasmas (mean of 3 laboratories: 1.42 vs 1.48 for A and 1.22 vs 1.20 for B). The between-laboratory precision of the calibration with lyophilized plasmas was not considerably different from that with fresh plasmas (CV for 3 labs: 5.2% vs 6.8% for A and 0.9% vs 2.2% for B). The ISI estimated with lyophilized plasmas on results of day 1 were not different from those of days 2 through 10. Good within-laboratory precision of the calibration (CV around 2%) was already achieved on day 3. In conclusion, this study shows that lyophilized plasmas pooled from normals and patients on oral anticoagulants can be used as substitutes for individual fresh plasmas to simplify the existing procedure for thromboplastin calibration.

Anticoagulants↗
PubMed1996

European Concerted Action on Anticoagulation (ECAA)-the multicentre calibration of rabbit and human ECAA reference thromboplastins. Steering Committee.

Two candidate ECAA reference preparations have been calibrated in a multicentre exercise at 14 representative national laboratories to provide reference thromboplastin for a large field study in 16 European countries. Two preparations were required because of the established differences in ISI arising from the two main routes of calibration via rabbit and human IRP. To be comparable with working reagents in everyday use a human plain recombinant reagent of low ISI and a rabbit plain preparation of moderately high ISI were selected. A precise calibration of the two candidate preparations has been achieved with the manual PT technique and an ISI of 0.95 (SE 0.0078) for the human reagent and 1.67 (SE 0.0322) for the rabbit reagent.

Animals↗
PubMed1995

A partial factor V deficiency in anticoagulated lyophilized plasmas has been identified as a cause of the international normalized ratio discrepancy in the external quality assessment scheme.

Lyophilized normal and anticoagulated plasmas are increasingly used in External Quality Assessment schemes (EQAS) to assess the quality of performance of laboratories engaged in the control of oral anticoagulant therapy by means of the International Normalized Ratio (INR) system and for the standardization of the prothrombin time (PT). The main feature of the INR system is that the value measured for an individual plasma should be independent of the reagent used. This holds true only if the variable factors influencing the responsiveness of the reagents are the vitamin K-dependent clotting factors, the other factors being constant and within normal limits. We provide evidence that even a partial factor V (FV) deficiency (FV activity < 60 U/dl) in anticoagulated plasmas can be responsible for discrepancies between INR values as measured for a single lyophilized or fresh plasma by different reagents and that the discrepancy is proportional to and magnified by the International Sensitivity Index (ISI) of the reagent used. The greater the difference between ISI values, the wider the gap between INR values. Since FV is one of the most labile plasma clotting factors, its activity is likely to be lost during freeze-drying. Hence, we recommend a thorough control of the FV activity in commercial and home-made lyophilized plasmas before their use in EQAS and in the standardization of the PT.

Blood Banks↗
PubMed1994

Results of a collaborative study for fibrinogen measurement. Evidence that the use of a common calibrator improves interlaboratory agreement.

One hundred and sixty-five laboratories were asked in two different surveys to perform duplicate fibrinogen measurements on the same lyophilized plasmas by their own methods and reagents and two different methods of calibration. The between-laboratory variability, expressed as coefficient of variation (CV), and the extent of between-method and between-reagent differences were taken as a measure of agreement between measurements. It was found that the overall between-laboratory range of CV values was 9-16% and that it could be improved if a common calibrator was used. The improvement was more pronounced for the thrombin time-derived (Clauss) method (average CV reduction 43%) than for the prothrombin time (PT)-derived method (average CV reduction 12%). A satisfactory agreement was found between the PT-derived and the Clauss method for the normal-PT plasma, whereas the PT-derived was slightly higher than the Clauss method for the abnormal-PT plasmas, irrespective of calibration. There were statistically significant between-reagent differences within the Clauss method, which were reduced if the common calibrator was used. In conclusion, the results shows that a system of common calibration for fibrinogen determination improves interlaboratory agreement by reducing the CV and minimizing between-reagent differences, particularly for the Clauss method. The authors recommend manufacturers of reagents to link their calibrators to the International Standard for fibrinogen.

Calibration↗
PubMed1994

Results of a multicenter study assessing the status of standardization of a recombinant thromboplastin for the control of oral anticoagulant therapy.

An international collaborative study involving 20 laboratories was undertaken to evaluate the status of standardization of a commercial recombinant thromboplastin. The results show that the reagent fulfills the WHO requirements for thromboplastin calibration against two International Reference Preparations (IRP) from different species, because there was a linear relationship of log-transformed prothrombin times as measured by the recombinant reagent and the two IRPs in normal individuals and patients stabilized on oral anticoagulants. The regression lines drawn through the patient data points passed through the normal data points in the majority of instances. The average ISI values for three different batches were close to unity. On the average, the ISI value calculated against BCT/253 (human, plain) was slightly smaller than that against RBT/79 (rabbit, plain). The between laboratory precision of calibration (CV = 5-6%) did not change whether BCT/253 or RBT/79 was used, whereas it was substantially improved when the calibrations of batches 2 and 3 were performed against batch 1, arbitrarily taken as standard (CV < or = 1.7%). Statistical analysis to test for differences between slopes revealed no significant between-batch differences in 16 of 20 laboratories. However slight differences for the third batch (2.8% less than the average ISI value of batches 1 and 2) leave room for further improvement in the standardization of the reagent.

Animals↗
PubMed1994

Clinical manifestations and management of inherited thrombophilia: retrospective analysis and follow-up after diagnosis of 238 patients with congenital deficiency of antithrombin III, protein C, protein S.

The clinical history of 238 patients with inherited thrombophilia (AT III = 94, PC = 103, PS = 41) was analyzed retrospectively at diagnosis and in the follow-up period after diagnosis. At diagnosis 129 patients (54%) had suffered from thrombosis, with a recurrence rate of 48%. The most frequent onset manifestation was deep vein thrombosis of lower limbs (58%). Thrombotic history started before 40 in 80% of the cases. Forty-nine percent of the venous thromboses were preceded by a triggering event, in most cases pregnancy (17%) and surgery (12%). After diagnosis, follow-up lasted a total of 1,113 pt-years. A policy of short-term prophylaxis during risk situations for all patients and long-term prophylaxis in symptomatic patients failed to prevent venous thrombotic episodes (diagnosed by objective methods) in 4 previously asymptomatic subjects and recurrence in 7 previously symptomatic subjects. After knowledge of the patients' diagnosis the incidence of venous thrombosis/100 pt-years was reduced as compared before diagnosis as total episodes (onset+recurrencies) (1.0 vs 1.9), onset episodes (0.7 vs 1.3) and recurrent episodes (1.3 vs 4.8), even though the differences were not statistically significant. However most of the venous thromboses occurred at a more advanced age (67% after 40 years) and without any apparent cause (83%), at significant variance with the period preceding the diagnosis; in particular the incidence of venous thrombotic onset in patients younger than 40 passed from 1.3/100 pt-years to 0.2/100 pt-years. In 6 recurrences after diagnosis a poor compliance for antithrombotic treatment was recognized.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Multicentric evaluation of a new PT reagent based on recombinant human tissue factor and synthetic phospholipids.

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)

Animals↗
PubMed1994

Poor comparability of prothrombin fragment 1 + 2 values measured by two commercial ELISA methods: influence of different anticoagulants and standards.

We compared F 1 + 2 results obtained with two commercial ELISA methods (Behring and Baxter) assaying the same plasma samples. There was little correlation between the results of the two methods, as shown by the low correlation coefficient (r = 0.50) and by low percentage of concordant classification (normal or abnormal) of the samples (24%). Such poor correlation is probably due to the different anticoagulants suggested, because correlation improved when both methods were carried out in plasmas collected with the same anticoagulant. However, the Baxter method still gave significantly lower F 1 + 2 values than the Behring method. Assuming that this difference is due to the use of standards with different F 1 + 2 concentrations, the standards from Behring and Baxter were evaluated by both methods. Parallel dose-response curves were obtained when the standards were run by the Behring method but not by the Baxter method, indicating that the two standards are qualitatively different. This study demonstrates that the two F 1 + 2 methods give different values for the same samples and that these values are poorly correlated. Standardization of the F 1 + 2 assays cannot be achieved easily simply by using a common standard and the use of different anticoagulants appears to be the main reason for poor standardization.

Adolescent↗
PubMed1993

Comparison of functional assays for protein S: European collaborative study of patients with congenital and acquired deficiency.

Four functional assays for protein S were evaluated by 4 different laboratories, each center using its own method. The aim of this study was to compare these different assays and to establish a relationship with results of immunological assays of total and free protein S antigen and C4bBP. The same plasma samples were distributed to each center and tested in blind. In 47 normal subjects, there was no significant difference between the 4 functional assays, with mean values ranging from 93 to 100%. These values were in good agreement with those of free and total protein S antigen. In 34 patients with a quantitative congenital deficiency of protein S the mean values of protein S activity were decreased with the 4 assays, ranging from 25 to 40%. Free protein S antigen was reduced to a similar extent, whereas total antigen was either normal or decreased. The correlation of protein S activity with free protein S antigen was satisfactory for 3 methods, with coefficients of correlation varying from 0.84 to 0.92 whereas it was only 0.70 in one lab. When total protein S antigen was reduced, protein S activity was decreased in all the patients with the 4 assays. In contrast when total protein S antigen was normal an important overlap of protein S activity between normals and patients was observed in one lab with 12 patients misclassified. In 8 patients with a functional defect, results of protein S activity differed substantially according to the assay used and about half of these patients were misclassified.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1993

Are capillary whole blood coagulation monitors suitable for the control of oral anticoagulant treatment by the international normalized ratio?

The 512 Coagulation Monitor is a portable coagulation photometer that uses disposable cartridges containing a lyophilized rabbit brain thromboplastin to measure the PT for capillary whole blood. It has been proposed as a suitable system for patient self monitoring at home, but its performance has never been thoroughly assessed for results expressed as International Normalized Ratio (INR). In particular, there is no available information about the adequacy of the WHO calibration model with the Monitor. The aims of the study were to determine the International Sensitivity Index (ISI) against the secondary International Reference Preparation for rabbit thromboplastin and to assess the precision of the INR. The study demonstrates that the Monitor can be calibrated with the WHO model, because log-transformed PTs for patients stabilized on oral anticoagulants and normal individuals are linearly related and because the same orthogonal regression line describes patient and normal data points adequately. However, the ISI calculated in this study (2.715) is higher than that adopted by the manufacturer (2.036). The between-assay reproducibility of the Monitor is acceptable (CV = 9.7%) with results expressed in seconds, but become unacceptably poor when the results are converted into INR (CV = 18.8%) because of the high ISI value of the thromboplastin used. We think that the Monitor might be suitable for monitoring oral anticoagulant therapy if the manufacturer would provide a more sensitive thromboplastin in the cartridges.

Administration, Oral↗
PubMed1993

Effects of hirudin on activated partial thromboplastin time determined with ten different reagents.

Hirudin prolongs the APTT when added to normal plasma and the extent of prolongation depends on the type of reagent used. The aim of this study was to compare the dose-response curves of 10 widely used APTT reagents for linearity and parallelism. On each of 10 working days a normal pooled plasma was mixed with increasing amounts of recombinant hirudin (HBW023) ranging from 0 to 5 micrograms/ml and tested for APTT by photo optical coagulometer. Within each working day, clotting times were measured in duplicate and the order of testing with each reagent was changed every day. Results were expressed as ratios of clotting times with hirudin to clotting times without hirudin, and the values plotted against the hirudin concentration on a log-log scale. The dose-response curves for all reagents were linear over 0.3-1.2 micrograms/ml. The reagent-related slopes ranged from 0.225 +/- 0.003 to 0.303 +/- 0.003 (mean +/- SE) and were significantly different. Precision studies indicated that the least sensitive reagent was also the least precise. These findings indicate that the clotting time values obtained for patients treated with hirudin will vary depending on the APTT reagent used.

Blood Coagulation↗
PubMed1993

Ischemic stroke in congenital (type II C) defective antithrombin III.

Type II C is a subtype of defective antithrombin III deficiency in which there is a molecular defect in the heparin binding site. Usually, heterozygous patients with this defect have little or no thrombotic symptoms. Ischemic stroke has never been described. We report the case of a young woman who had an episode of right-sided hemiparesis. The computed tomographic scan showed an ischemic lesion in the left hemisphere. There were no previous thrombotic episodes in the patient's history and the sole risk factor for thrombosis was taking of an oral contraceptive. Her family history was midly positive for thrombosis (superficial thrombophlebitis in two relatives). Laboratory tests showed normal antithrombin III antigen, low heparin cofactor activity and an increased slow-moving peak in crossed-immunoelectrophoresis with heparin. The same pattern was found in 7 of 20 relatives. Thus, a diagnosis of congenital type II C defective antithrombin III was made. This report suggests that young patients with ischemic stroke should be screened for defective antithrombin III.

Adult↗
PubMed1993

Markers of procoagulant imbalance in patients with localized melanomas and autoimmune disorders.

Hypercoagulability can be defined as a condition of procoagulant imbalance due to heightened enzymatic activation of coagulation zymogens, but with no laboratory evidence of fibrin deposition nor clinical signs of thrombosis. The imbalance can be detected by measuring the plasma levels of prothrombin fragment 1 + 2 (F1 + 2), fibrinopeptide A (FPA) and thrombin-antithrombin III (TAT) complexes. The aims of this study were to establish the frequency of existence and biochemical pattern of hypercoagulability in patients with cancer and autoimmune disorders, clinical conditions associated with an increased risk of thrombosis, and to ascertain the most sensitive method for its diagnosis. In approximately one-fourth of the patients hypercoagulability was identified by finding high levels of FPA F1 + 2 or TAT unaccompanied by signs of fibrin deposition (expressed by normal levels of D-dimer). In a smaller proportion of patients (approximately 10%), the concomitant presence of high levels of D-dimer indicated that the activation of the coagulation cascade had gone beyond the stage of heightened enzymatic activity to the point of cross-linked fibrin deposition. Of the markers used to detect hypercoagulability. FPA seems to be the most sensitive, being significantly increased in all clinical conditions studied.

Adolescent↗