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PubMed1984

Clinical evaluation of a fully automated chromogenic method for prothrombin time compared with a conventional coagulation method.

The clinical usefulness of a chromogenic method for prothrombin time (PT) determination has been assessed in a wide range of clinical conditions, and it is compared with the conventional clotting method for PT. The new method appears to be as sensitive as the clotting PT to deficiencies of clotting factors of the extrinsic and common pathway, except for fibrinogen. Patients with proven liver disease were correctly diagnosed with a prevalence of abnormal results comparable to that by the clotting PT. Results by the two methods correlated highly (r = 0.96) for normal and congenitally deficient plasmas as well as for plasmas from patients on oral anticoagulant treatment (r = 0.95). High reproducibility (between-assay CV less than 3%) and easy adaptation to centrifugal analyzers make it a suitable candidate to replace the conventional method.

Adolescent↗
PubMed2000

A comparison between capillary and venous blood international normalized ratio determinations in a portable prothrombin time device.

The CoaguChek PT system is a portable point-of-care device for prothrombin time testing that can be used with capillary and venous whole blood. This system had been calibrated by the manufacturer in terms of the international normalized ratio (INR) for monitoring oral anticoagulant therapy. The purpose of the present study was to compare capillary blood with venous blood INRs from healthy volunteers and patients treated with oral anticoagulants using the same CoaguChek PT system. Two different CoaguChek PT strip formulations [international sensitivity index (ISI), 1.5 and 1.1] were used in separate test series. The differences between capillary and venous blood INRs were statistically significant (P < 0.001) but the magnitude of the differences was small. The mean relative deviations of the INR were 5.8 and 2.8% for the strips with ISI 1.5 and 1.1, respectively. These deviations are clinically acceptable. It is concluded that capillary blood can be replaced by venous blood for the calibration of the CoaguChek PT system.

Anticoagulants↗
PubMed1984

Inhibition of the cold activation of Factor VII and the prothrombin time.

Normal whole blood, collected and stored in borosilicate or commercial siliconized borosilicate tubes at 4 degrees C, undergoes a time-dependent activation of Factor VII and a shortening of the prothrombin time (PT). Addition of inhibitors to Factor XII fragments (corn Hageman factor inhibitor, CHFI) or to activated Factor XII (Cytochrome-C) inhibited in a concentration-dependent way the cold-promoted activation of Factor VII and the shortening of the PT. When celite was added to whole blood in polypropylene tubes at 4 degrees C, Factor VII was activated and the PT shortened. Preincubation of celite with CHFI or Cytochrome-C prevented the activation of Factor XII and the subsequent activation of Factor VII and the PT. These studies demonstrate the importance of Factor XII in the cold activation of Factor VII and shortening of the PT and indicate that inhibitors to activated Factor XII or XII fragments are useful in inhibiting in vitro shortening of the PT. These findings suggest that the development of a collection tube that prevents contact activation also would inhibit adequately the cold-promoted activation of the PT and Factor VII.

Aprotinin↗
PubMed2005

Clinically relevant differences in prothrombin time and INR values related to blood sample collection in plastic vs glass tubes.

We compared prothrombin times (PTs) and international normalized ratios (INRs) for blood samples drawn into plastic vs glass collection tubes. We collected 60 venous blood samples into 4.5-mL glass and 2 plastic tubes (2.7 and 3.5 mL). An additional 153 samples, including 63 from warfarin-anticoagulated patients, were collected only in glass and 2.7-mL plastic tubes. The PTs and INRs were determined following routine laboratory procedures. A subset of 35 frozen aliquot samples was analyzed with a different instrument-reagent combination. The PTs and INRs for samples in plastic tubes were significantly lower than for samples in glass tubes. The mean INR differences increased with INR magnitude from approximately -0.1 (INR, 1.5) to -0.7 (INR, 4.5). Of the plastic tube INRs, 50% were more than 10% lower than INRs from samples collected in glass tubes. Therapeutic monitoring based on plastic-tube INRs could result in higher doses of warfarin.

Blood Specimen Collection↗
PubMed1993

Standardizing the prothrombin time. Calibrating coagulation instruments as well as thromboplastin.

Recently, indications for anticoagulation with warfarin have increased, prothrombin time (PT) monitoring at offices and homes has become available, and the international sensitivity index (ISI) has been recognized as a means of adjusting for differences in thromboplastins to standardize warfarin sodium dosing. However, different coagulation instruments may yield differences in PTs even after correcting for the ISI by means of the international normalized ratio (INR) (INR = [PT measured ISI/PT normal]). Because the PTs and INRs from our Anticoagulation Clinic (portable PT monitor, ISI = 2.04, normal PT = 12.0 seconds) differed from the hospital reference laboratory (ISI = 2.01, normal PT = 12.0 seconds) despite nearly identical ISIs and equivalent control or normal PTs, we systematically compared the two systems. During a 3-month period, we studied two groups of 50 consecutive patients who had been receiving a stable dose of warfarin. After a single venipuncture, PTs and INRs were measured independently, and regression lines were calculated. Within each group, the results from the different instruments were not identical, but they were highly correlated. In comparing INRs, the regression lines for the separate and combined groups were as follows: group 1 monitor INR = 0.49 reference INR + 0.81, r = .94; group 2 monitor INR = 0.57 reference INR + 0.86, r = .88; and combined monitor INR = 0.49 reference INR + 0.95, r = .89. Only 82% of the differences for all samples were within 1.0 INR units. We concluded that the instrumentation effect may be clinically meaningful, and coagulation instruments as well as thromboplastins should be calibrated to standardize warfarin therapy.

Blood Coagulation Tests↗
PubMed2000

Accuracy of a portable prothrombin time monitor (Coagucheck) in patients on chronic oral anticoagulant therapy: a prospective multicenter study.

A portable prothrombin time (PT) monitor allows patients on oral anticoagulant therapy (OAT) to measure their PT at home. The purpose of the study was to evaluate the accuracy and precision of a portable PT monitor (Coagucheck, Roche Diagnostics, Mannheim, Germany) as compared with laboratory methods. The prospective study was conducted in four centers of the Italian Federation of Anticoagulation Clinics. A one-month instruction phase was followed by a six-month surveillance phase. Seventy-eight subjects on stable OAT (48 men, 30 women, age range: 18-75) were selected on a volunteer basis. Dual measurements of INR values were performed in each subject both from finger capillary blood by the monitor and from venous blood by the Anticoagulation Clinic laboratory in three instruction sessions. The mean difference (bias) of the monitor INR results when compared with the average of laboratory INR and monitor INR results was -0.025 (limits of agreement-LA: -0.84/+0.81 INR units). The mean bias was -0.0675 (LA: -0.37/+0.23), +0.018 (LA: -0.39/+0.35), and +0.039 (LA: -0.49/+0.55), respectively, for INR values lower than 2.0, between 2.0 and 3.0, and greater than 3.0. The overall precision coefficient of monitor INR was 0.370, while it was 0.23, 0.46, 0.29, and 0.21, respectively, in Centers 1, 2, 3, and 4. The overall variation coefficient was 6.5% while it was 3.7%, 8.5%, 4.7%, and 4.9%, respectively, in Centers 1, 2, 3, and 4. Coagucheck has an acceptable level of accuracy for INR values in the range between 2.0 and 3.0. A wide variation in monitor performance was found among centers.

Administration, Oral↗
PubMed1983

Biopotency of vitamin K. I. Antihemorrhagic properties of structural analogs of phylloquinone as determined by curative prothrombin time tests.

Relative antihemorrhagic properties of structural analogs of transphylloquinone (vitamin K1) have been determined by curative prothrombin time tests with vitamin K-deficient chicks. Analogs (where applicable) and the phylloquinone standard had (all-) rac-trans configuration, and all compounds were well characterized (structure, purity, trans: cis). Compounds were administered as single oral doses according to the up-and-down procedure. Estimation of mean effective doses allowed a reliable calculation of relative activities for analogs in comparison with vitamin K1 standard. 2', 3'-Dihydro-phylloquinone had a relative activity of only 6.7%, i.e. it was about 15 times less active than phylloquinone. Further reduction of this analog led to 2',3',5,6,7,8-hexahydro-phylloquinone which was completely inactive. Analogs with oxygen functions in the side chain, 6'-hydroxy-K1, 6'-oxo-K1, and 7'-hydroxy-6'-oxo-K1, displayed relative activities of 20.5%, 31.9%, and 30.5%, respectively. Phylloquinone-2,3-epoxide was 1.7 times more active than the phylloquinone standard. An analog with a 7-carbon side chain ending with a carboxy group (in mammals a urinary metabolite of vitamin K1) and its corresponding ethyl ester derivative were practically inactive.

Animals↗
PubMed1976

An evaluation of the Lancer Coagulyzer in the measurement of the one-stage prothrombin time.

An evaluation of a photoelectric clot timer, the Lancer Coagulyzer, in measuring the one-stage prothrombin time has been carried out. The machine is considered to provide reliable results on correctly taken samples without interference by plasma bilirubin, only rarely failing to detect clotting in turbid plasma using a wide range of thromboplastins. The apparatus is useful where there is a sufficient number of samples to be tested.

Bilirubin↗
PubMed2000

A comparison of INRs determined with a whole blood prothrombin time device and two international reference preparations for thromboplastin.

Oral anticoagulant therapy is usually monitored with the prothrombin time (PT) on citrate plasma samples. In recent years instruments have been developed for measurement of the PT in non-citrated whole blood. In the present study, the manufacturer's calibration of one type of device (CoaguChek) in terms of the international normalized ratio (INR) was evaluated by one laboratory. Three subsequent lots of test strips for the CoaguChek were investigated using blood samples from 56 coumarin-treated patients. Citrated plasma samples from the same patients were analysed with two international reference preparations for thromboplastin (IRP), i.e., rTF/95 (recombinant human) and RBT/90 (rabbit brain). There were statistically significant INR differences between CoaguChek and the international reference preparations (p <0.001), but the mean relative deviation of the INR was not greater than 0.104. Clinically relevant criteria were used to assess the agreement between the CoaguChek and the IRP results. Standard agreement ranged from 82% to 95%. It is concluded that these test strips achieved a clinically acceptable level of accuracy. Further studies of patient management with these strips are justified.

Administration, Oral↗
PubMed1994

Optimization of the dilute prothrombin time for the detection of the lupus anticoagulant by use of a recombinant tissue thromboplastin.

The dilute prothrombin time (dPT) is a widely accepted sensitive screening test for the lupus anticoagulant (LA). In general, Simplastin (Organon Teknika), a rabbit brain thromboplastin, diluted 1/500, is used in this test. Recently, human tissue thromboplastin obtained by recombinant DNA technology has become available and we have evaluated the usefulness of one such preparation, Innovin (Dade), for the detection of the LA. dPTs, using several dilutions of Innovin were determined on plasmas from 18 normal individuals and 15 patients with a well-documented LA. The dPT ratios, calculated as the individual result divided by the mean normal, were statistically compared. Innovin in dilutions from 1/100 onwards was found to be significantly more responsive to the LA than Simplastin (P < 0.05). Intra-assay coefficients of variation (CVs) ranged from 1.05% to 14.8% with Innovin, versus 2.7%-24.3% with Simplastin (P < 0.05); inter-assay CVs ranged from 5.6%-11.8% with Innovin, versus 4.2%-33.8% with Simplastin (P < 0.001). Analysis of 316 consecutive plasma samples from non-anticoagulated patients, on which a LA determination was requested, showed a 100% sensitivity and a 96% specificity of the dPT performed with Innovin, as compared to 81% and 93% respectively for the dPT using Simplastin.

Antiphospholipid Syndrome↗
PubMed1994

The influence of the reference mean prothrombin time on the international normalized ratio.

The International Normalized Ratio (INR) is a mathematical transformation of the prothrombin time (PT). The transformation requires a laboratory to compute the geometric mean of its own reference population. In this paper, the authors examine how the reference mean PT influences the INR accuracy and precision using a validated probabilistic model. The variance of the geometric mean of reference populations in three laboratory settings was determined. Because the variance of an individual laboratory geometric mean is not directly determinable by simple parametric equations, its variance is estimated using bootstrap analysis. The geometric mean is compared to the computationally simpler arithmetic mean for effects on accuracy and precision of the resulting INR. The study shows mathematically and empirically that using the arithmetic mean biases INR determinations so that patients tend to be over-anticoagulated. However, in the laboratory settings examined, the amount of bias was both statistically and clinically insignificant. An analysis of the effect on the INR of errors in estimating the geometric mean reference PT also is performed. For large biases in estimating the reference mean, the INR can be significantly affected and can trigger inappropriate clinical actions in patients. The authors demonstrate empirically and mathematically that biases in the geometric mean reference PT do not affect the INR coefficient of variation. However, they produce significant differences in confidence intervals for INR determinations. Laboratories must exercise care in determining specific reference means to ensure that biases do not occur in geometric mean reference PT determinations. This can be achieved by circumspection in the selection of normal subjects for the reference population, carefully reviewing the data, and performing the proper calculations on the data.

Female↗
PubMed2004

Comparison between CoaguChek S- and Owren-type prothrombin time assay for monitoring anticoagulant therapy.

INTRODUCTION: Anticoagulation therapy with warfarin is monitored by the prothrombin time (PT) assay. The PT is standardized using international normalized ratios (INRs). By keeping the INR within specific values, it is possible to reduce potential complications from the treatment. To facilitate the PT monitoring, point-of-care devices suitable for capillary whole blood measurements have been developed. The aims of this study were to compare the INR values obtained by such a device, CoaguChek S, with those obtained from the Owren-type PT assay and to evaluate the differences seen. MATERIALS AND METHODS: In 351 consecutive warfarin-treated patients, INR was measured in capillary whole blood samples with CoaguChek S and was compared to venous plasma samples analyzed with the Owren PT method. Sixty-nine of these patients, including those deviating the most between the methods, were further evaluated according to levels of factor II (prothrombin), factor V, factor VII, factor X, fibrinogen, activated partial thromboplastin time (aPTT) and antiphospholipid antibodies. RESULTS: The results from CoaguChek S produced a correlation coefficient of 0.81 to the Owren-type PT assay and a concordance of 85.2%. Factor V and fibrinogen correlated significantly (p<0.05) to the degree of deviation between the methods. The presence of antiphospholipid antibodies did not influence the degree of deviation between the two methods. CONCLUSIONS: INR analysis of whole blood with CoaguChek S is comparable with INR measured in plasma with Owren chemistry. The activities of factor V and fibrinogen contribute to the deviation seen between the methods. Differences in sensitivity to antiphospholipid antibodies could not be demonstrated.

Anticoagulants↗
PubMed1990

Predicting the daily prothrombin time response to warfarin.

Our objective was to evaluate the effectiveness of a computer program to predict daily prothrombin time (PT) response to warfarin therapy using prospectively collected data. The program's predictive performance (precision) and accuracy (bias) were evaluated using fraction mean absolute error and fraction mean error, respectively. We analyzed data from 40 patients using from zero to nine PT feedbacks. The fraction mean absolute error varied from 0.058 to 0.13. The program utilized a pharmacokinetic/pharmacodynamic Bayesian forecasting system to predict prothrombin response.

Aged↗
PubMed1984

Automated prothrombin-time test with use of a chromogenic peptide substrate and a centrifugal analyzer.

We modified a test for prothrombin time, to automate its performance by centrifugal analysis. The sample is activated with calcium-thromboplastin in the presence of a thrombin-specific chromogenic peptide substrate, Tos-Gly-Pro-Arg-p-nitroaniline (Chromozym TH). The endpoint of the reaction is set as the time after onset until a defined amount of substrate has been cleaved, as reflected in a fixed change in absorbance. The assay is as sensitive as clotting-type methods are to the clotting factors of the extrinsic pathway--except for fibrinogen, which can be estimated from the maximum absorbance difference. Substrate concentration has little effect on the result, and varying it does not significantly change the sensitivity to factor X, which indicates little interference with the enzymes of the coagulation cascade. The method was applied to the Cobas Bio centrifugal analyzer. An external calculator must be used to convert absorbance readings into reaction times, which can be expressed as percent-of-normal values or as "ratios" by use of reagent-specific factors. CVs were less than 2% within run, less than 6% day to day. Overall correlation with the clotting test (r = 0.95) was good. Using the Cobas Bio, we achieved a throughput rate of 200 samples per hour.

Autoanalysis↗
PubMed1994

In vitro reversal of heparin effect with heparinase: evaluation with whole blood prothrombin time and activated partial thromboplastin time in cardiac surgical patients.

This study was designed to evaluate the potential in vitro use of heparinase to eliminate functionally active heparin prior to performing whole blood (WB) prothrombin time (PT) and activated partial thromboplastin time (APTT) assays. A total of 250 U/kg of heparin for cardiopulmonary bypass (CPB) was administered to 30 cardiac surgical patients in three consecutive, divided doses (20, 80, and 150 U/kg) at 15-min intervals. Blood specimens were obtained prior to heparin administration (baseline) and 10 min after each heparin dose. After collection, blood specimens were fractionated into three aliquots of which the first was used for determination of heparin concentration. After gentle mixing, WB PT and APTT measurements were performed for heparinase (Aliquot 2)- and nonheparinase (Aliquot 3)-treated blood. With consecutive heparin doses of 20 and 80 U/kg, WB PT increased from a baseline of 12.3 +/- 0.1 s to 13.3 +/- 0.2 and 18.5 +/- 1.3 s, while WB APTT increased from a baseline of 28.3 +/- 1.1 s to 89.5 +/- 5.4 after the initial heparin dose (20 U/kg). When compared to baseline (no heparin) results, small, progressive increases in heparinase-treated WB PT (0.7 +/- 0.1, 1.5 +/- 0.1, 2.1 +/- 0.1 s) and APTT (2.3 +/- 0.3, 5.7 +/- 0.4, 9.5 +/- 0.5 s) were seen with increasing heparin concentration (0.23, 1.58, and 3.95 U/mL, respectively). Heparinase was highly effective in eliminating the anticoagulant effects of even large amounts of heparin in plasma from cardiac surgical patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗