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PubMed1981

Effect of thromboplastin and instrumentation on the prothrombin time test.

Prothrombin time was measured in three different plasma samples by 2580 laboratories in the 1977 CAP Proficiency Testing Program. Analysis of variance was used to show that instrument, as well as thromboplastin, has a significant effect upon observed prothrombin time. In addition, the instrument and thromboplastin effects were estimated, and all were shown to be linearly related to the prothrombin time of the plasma sample. This linear relationship was used to develop a formula for adjusting/correcting an observed prothrombin time for both the thromboplastin and instrument effect. This adjustment/correction method seems promising on the basis of its use in four different sets of data.

Hematologic Tests↗
PubMedDate not supplied

Effect of ingestion of glucose on fibrinolytic activity and prothrombin time in diabetic and non-diabetic persons.

Effect of ingestion of 50 g of glucose on euglobulin clot lysis time and prothrombin time was studied in 14 diabetic and 12 non-diabetic persons. There was no significant change in euglobulin clot lysis time and prothrombin time after ingestion of glucose in the non-diabetic group. In the diabetic group, ingestion of glucose resulted in significant increase in euglobulin clot lysis time at the end of one hr which returned to initial level at the end of two hours even though blood glucose level at two hrs was still higher than fasting level. Increase in clot lysis time has no correlation to the blood glucose level. There was no significant change in prothrombin time after glucose ingestion.

Blood Glucose↗
PubMed1987

A novel whole blood capillary technic for measuring the prothrombin time.

The prothrombin time (PT) is frequently performed to monitor anticoagulant therapy. Although relatively simple to perform, it requires venipuncture and laboratory resources for sample handling and analysis. A recently developed capillary whole blood device that uses fingerstick samples was evaluated. Paired capillary whole blood and reference plasma PTs were performed in 858 samples from 732 subjects. The PT for normal volunteers (n = 193) was 11.8 +/- 0.9 seconds with the use of the new instrument and 12.1 +/- 0.5 seconds with the use of the reference method. In samples from 539 patients receiving anticoagulants, the correlation coefficient between the two methods was 0.96. Venous whole blood without anticoagulant and capillary whole blood gave equivalent results, which suggests that the fingersticks do not effect the quality of the specimen. Variation in hematocrit between 23.4% (0.34) and 53.8% (0.538) did not alter the performance of the instrument. The new instrument is easy to use and may allow testing by nonlaboratory personnel and patients. It obviates the need for venipuncture, provides immediate results, and appears to be comparable in accuracy to current reference methods.

Anticoagulants↗
PubMed1990

Prediction of vitamin K response using the Echis time and Echis-prothrombin time ratio.

Echis carinatus venom contains proteases capable of activating both normal and descarboxy prothrombin. We showed this venom (Sigma) principally activates prothrombin with almost no factor X activation. Echis time in combination with prothrombin time can predict vitamin K responsiveness since the Echis time is usually normal in the presence of descarboxy prothrombin associated with vitamin K deficiency. 38 patients with abnormal routine prothrombin times (PT) had both coagulant and immunogenic factor II assays along with Echis times done before and after vitamin K. Of 22 patients responding to vitamin K, based on correction of PT, 21 had normal initial Echis times and of 16 not responding, 11 had abnormal Echis times, giving a sensitivity of 95.4% and specificity of 68.8% for vitamin K responsiveness. 90% of patients with a PT/Echis time ratio less than 1.3 and a prolonged Echis time did not correct their PTs with vitamin K therapy. The 5 non-responders with normal Echis times all showed normal initial coagulant and antigenic prothrombin, but 3 had low F V and/or F VII.

Blood Coagulation Disorders↗
PubMed1995

Aprotinin prolongs whole blood activated partial thromboplastin time but not whole blood prothrombin time in patients undergoing cardiac surgery.

Aprotinin is being used increasingly to limit cardiopulmonary bypass (CPB)-induced coagulation derangements. Since whole blood prothrombin time (PT) and activated partial thromboplastin time (APTT) assays are beneficial in the treatment of bleeding after CPB, we studied the potential effect of aprotinin on these whole blood assays. Blood specimens from 151 cardiac surgical patients were obtained in two phases: prior to heparin administration, before CPB, and subsequent to heparin neutralization after CPB. After collection, blood specimens were divided into two aliquots and mixed with either normal saline (NS) or aprotinin (A, 200 or 400 Kallikrein inhibiting units (KIU)/mL). Whole blood specimens were used to measure whole blood PT and APTT using CoaguChek Plus instruments. Whole blood PT results were similar between normal saline. (NS)- and aprotinin-spiked specimens before CPB (A, 12.9 +/- 1.5s; NS, 12.8 +/- 1.5s; P = 0.76) and after CPB (A, 17.5 +/- 2.4s; NS, 17.7 +/- 2.4s; P = 0.58). In contrast, whole blood APTT results were prolonged in aprotinin-spiked specimens prior to CPB (A, 63.3 +/- 32.2s; NS, 38.6 +/- 16.3s; P < 0.0001) and after CPB (A, 65.9 +/- 23.7s; NS, 45.7 +/- 14.4s; P < 0.0001). A dose-dependent prolongation of whole blood APTT by aprotinin was demonstrated by a greater mean difference in APTT (P = 0.0001) between specimens spiked with NS or 200 KIU (17.5 +/- 12.2s) vs 400 KIU (27.8 +/- 21.5s) of aprotinin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Evaluation of a new chromogenic substrate assay for the measurement of the prothrombin time.

The chromogenic prothrombin time assay Nycotest Chrom was evaluated and compared with another chromogenic assay (Chromoquick) and with the well-known coagulometric Thrombotest. The intra-assay variation of the test was satisfying both in the normal range (CV = 3.6%) and in the therapeutical range of oral anticoagulation (CV = 3.5%). These values were somewhat higher than those of the Chromoquick test (1.3% and 1.1%) and those of the Thrombotest (2.3% and 2.5%). The inter-assay variation coefficient amounted to 3.3% in the normal range and in the therapeutical oral anticoagulation range to 4.4%. The respective values for the Chromoquick test were somewhat lower (2.2% and 3.9%), those of the Thrombotest in the normal range were also lower (2.1%), and in the therapeutical range they were much higher (9.2%). The coefficients of correlation of the Nycotest Chrom test in the therapeutical range were highest when comparing them with those for the Chromoquick test (r = 0.97; p < 0.0001) and somewhat lower in comparison with the Thrombotest (r = 0.95; p < 0.0001). The results of the three methods paralleled also in the starting phase of oral anticoagulation treatment. Storage at 4 degrees C and at 25 degrees C showed good stability of the Nycotest Chrom reagent for up to 24h. We conclude that the Nycotest Chrom assay is well suited for the measurement with a centrifugal fast analyser, which is attractive on behalf of the usually large series of request for prothrombin time measurements when monitoring oral anticoagulation therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Warfarin therapy. The effect of heparin on prothrombin times.

Sharp decreases in the prothrombin time after discontinuing heparin have been reported in patients undergoing oral anticoagulant therapy. Twenty-five patients receiving continuous intravenously administered heparin and orally or intravenously administered warfarin were studied. All patients had prothrombin times greater than 1.40 times control, and activated partial thromboplastin times 1.5 to three times control before discontinuing heparin therapy. Prothrombin times on the heparin infusion and four to six hours after it was discontinued were compared. The mean change in the prothrombin time was -1.60 s with a range of +0.8 to -5.5 s. Eight (32%) of 25 patients had a decrease of greater than 2 s. The decrease in prothrombin time correlated poorly with heparin dose or activated partial thromboplastin time in patients taking heparin. Since the change in prothrombin time is unpredictable, a repeated prothrombin time is recommended after stopping heparin therapy prior to discharging a patient.

Adult↗
PubMedDate not supplied

Warfarin anticoagulation: difficulties in interpretation of the prothrombin time.

Studies of the prothrombin time in normals and patients receiving warfarin therapy revealed a marked shortening of the prothrombin time when the blood was collected in any type of collection tube other than a polypropylene tube. This shortening of the prothrombin time in patients receiving coumadin therapy was time and temperature dependent. This in-vitro shortening of the prothrombin time could lead to serious clinical errors involving dosage of warfarin derivatives to be administered to patients.

Anticoagulants↗
PubMed1975

Statistical comparison of the fibrometer and the Electra 600 for prothrombin time determination.

Determinations of prothrombin time with the semiautomatic fibrometer and with a more automated machine (Electra 600) were compared in regard to reproducibility, accuracy, and speed. Prothrombin times determined for replicate samples with the two machines showed a correlation coefficient of 0.98, but the Electra 600 sensed the clot 0.5 seconds before the fibrometer. The overall coefficients of variation for multiple tests in the normal therapeutic and elevated ranges of prothrombin time were 3.5% for the fibrometer and 2.0% for the Electra 600. The average technician working time was 60% shorter with the fully automated machine than with fibrometer. It is concluded that the automated machine was more accurate and more rapid in determining prothrombin time.

Automation↗
PubMed1979

The use of pooled patient plasma as an abnormal prothrombin time control.

Five abnormal prothrombin time pooled patient plasma samples and seven commercially prepared abnormal prothrombin time control plasmas were compared. A fibrometer was used to run prothrombin time tests from 8 to 51 days on individual aliquots of the pooled patient plasmas and individual vials of the commercial products. Pooled patient plasmas exhibited greater reproducibility with generally lower coefficients of variation than did the commercial products, with the added advantage that they reflected the patient population more directly. Almost all samples displayed a significant rise in mean clotting times during the testing period. However, the reasons for this rise are not entirely clear.

Analysis of Variance↗
PubMed1993

International standardization of laboratory control of oral anticoagulant therapy: a survey of thromboplastin reagents used for prothrombin time testing.

The prothrombin time (PT) test is the primary measurement in the laboratory control of oral anticoagulant treatment. The traditional expression of PT test results, either as percentage prothrombin activity or PT ratio, is inadequate for international communication and comparison because the values depend on the nature of the thromboplastin test system used. The WHO recommended universal scale of reporting PT results is based on calibration of local thromboplastin systems against an international reference preparation. This scale is the International Normalized Ratio (INR). Application of the INR scale in clinical practice should be encouraged by External Quality Assessment (EQA) schemes, which improve its precision. Many physicians are insufficiently aware of the different sensitivities of rabbit thromboplastins, which result in different anticoagulation intensities being employed in different clinics. Improvement in the situation can only be achieved by continuous education. The more widespread use of the INR scale should facilitate international comparison of anticoagulation results and eventually consensus on optimal target values. The introduction of the INR to countries not already using it, particularly the USA, should be strongly encouraged by all physicians with an interest in anticoagulation and especially those undertaking the long-term management of patients with prosthetic heart valves.

Animals↗
PubMed1984

Proficiency testing and standardization of prothrombin time: effect of thromboplastin, instrumentation, and plasma.

Prothrombin times accumulated from ten different proficiency testing surveys were analyzed in terms of a linear additive model described by Evatt et al (Clin Lab Haemat 1981; 3:331-342). Different types of lyophilized plasma samples were used, i.e., plasmas artificially depleted of coagulation factors by adsorption to aluminum hydroxide, and pooled plasmas of patients receiving coumarin drugs. For each plasma sample, both instruments and thromboplastins had a highly significant effect on the prothrombin time. For most instruments and thromboplastins, a good correlation was found between instrument effect or thromboplastin effect and the mean prothrombin time if various artificially depleted plasma samples from a single manufacturer were used. Artificially depleted plasmas from a second manufacturer gave different relationships between estimated effects and mean prothrombin time. Relationships based on lyophilized pooled patient plasmas were different from those of artificially depleted plasmas from either manufacturer. The potential use of the additive linear model for standardization of the prothrombin time in monitoring oral anticoagulant therapy is discussed. Additional studies are required to establish the suitability of this model to define a universal scale for prothrombin times of fresh plasma samples of anticoagulated patients. If suitable, the model can be linked to the International Normalized Ratio proposed by the World Health Organization.

Analysis of Variance↗
PubMed1992

Monitoring "mini-intensity" anticoagulation with warfarin: comparison of the prothrombin time using a sensitive thromboplastin with prothrombin fragment F1+2 levels.

Treatment with warfarin using a target International Normalized Ratio (INR) range of 1.7 to 2.5 is efficacious for many clinical indications, but the minimal intensity of anticoagulation required for antithrombotic protection has yet to be determined. To evaluate whether patients could be reliably monitored with a less intense regimen, we anticoagulated patients with warfarin for several months using a target INR range of 1.3 to 1.6 as determined by prothrombin time (PT) using a sensitive thromboplastin (Dade IS, International Sensitivity Index [ISI] = 1.3). Plasma measurements of F1+2, a marker of factor Xa action on prothrombin in vivo, were also obtained to determine the suppressive effect of warfarin on hemostatic system activity. Overall, 20 of 21 patients with a history of cerebrovascular events (mean age, 61 years) could be reliably regulated with warfarin in the target INR range. F1+2 levels were significantly suppressed from baseline in all patients, with a mean reduction of 49% (range, 28% to 78%). We found a significant relationship between the extent of suppression of prothrombin activation levels and the baseline measurements. A mean reduction of 65% was observed for those patients with baseline F1+2 greater than or equal to 1.5 nmol/L, but only 38% for baseline F1+2 less than or equal to 0.5 nmol/L. Overall, 68% of plasma samples obtained during stable anticoagulation were within the target INR range. PTs were also determined on all plasma samples with two thromboplastins of lower sensitivity (C+, ISI = 2.09; and automated simplastin, ISI = 2.10). Only 47% and 35% of PT determinations, respectively, were within the target range with these reagents. We conclude that prothrombin activation can be significantly suppressed in vivo with use of warfarin in an INR range of 1.3 to 1.6. This level of anticoagulation can be reliably achieved by monitoring PTs with a thromboplastin of high sensitivity.

Blood Coagulation↗
PubMed1995

Reference materials and reference measurement systems in laboratory medicine. Prothrombin time standardization: the problem of the control plasma.

The prothrombin time of fresh normal pooled plasma and the mean normal prothrombin time are currently recommended as the denominator term in the expression of prothrombin time ratios and International Normalised Ratio (INR) values. Fresh normal pooled plasma is also required for correct extrapolation of percent prothrombin time activity values. To avoid collection and measurement of a relevant number of normal individual samples for calculation of the mean normal prothrombin time or the necessity for a fresh plasma pool, lyophilised normal control plasma is made available by the manufacturers of thromboplastin reagents. The Verband der Diagnostica- und Diagnostikgerätehersteller (VDGH) has adopted a lyophilised normal pooled plasma (R82A) which was calibrated in two studies against fresh normal plasma pools and fresh individual normal plasmas, using a variety of plain and combined thromboplastins. Both studies concluded that plasma R82A could be used as a substitute for normal plasma, but a correction should be made for plain thromboplastin reagents. These data have been confirmed in an IFCC collaborative international study organised by the IFCC Working Group Standardisation of Coagulation Tests. In the latter study, in addition to plain and combined thromboplastin reagents, the recently introduced recombinant thromboplastins were evaluated and they showed a significant deviation from the sensitivity observed with extracted thromboplastins. Recombinant thromboplastins are under consideration as future international reference thromboplastins; the results of the IFCC collaborative study call for additional experimentation before this is accomplished.

Blood↗
PubMed1994

The influence of N-acetylcysteine on the measurement of prothrombin time and activated partial thromboplastin time in healthy subjects.

The purpose of the study was to evaluate whether the infusion of N-acetylcysteine decreased the measurement of prothrombin time and activated partial thromboplastin time (APTT) in healthy persons. N-acetylcysteine was administered intraveneously 10 mg kg-1 as a loading dose and then at a rate of 10 mg kg-1 h-1 for 32 h in six male subjects. The intrinsic, extrinsic and common pathway of coagulation were monitored with activated partial thromboplastin time (APTT), and prothrombin time, respectively. In addition, the extrinsic coagulation pathway was monitored with the clotting activity of single factors II, VII, and X. No effect on the intrinsic coagulation pathway was observed. There was a significant and rapid decrease in prothrombin time. Coagulation factors II, VII and X, the three components of prothrombin time, decreased significantly to different degrees. We conclude that infusion of N-acetylcysteine intraveneously decreases the prothrombin time in healthy subjects. Thus, one should not make conclusions which are too far-reaching based on prothrombin time alone in patients who have been treated recently with N-acetylcysteine intraveneously.

Acetylcysteine↗
PubMed1997

Plasma tissue factor antigen levels in capillary whole blood and venous blood: effect of tissue factor on prothrombin time.

To measure the amount of tissue factor released during specimen collection and its potential effect of shortening the prothrombin time, we measured tissue factor and prothrombin time in twenty-three paired venous and capillary blood samples from anticoagulated patients and in ten paired samples from controls. We also compared venous prothrombin time determined by a plasma-based assay with venous and capillary prothrombin time determined with a whole blood assay. Venous specimens were obtained using a two-syringe technique; capillary specimens were obtained by fingerstick after wiping the first drop of blood. Plasma tissue factor was determined by an enzyme-linked immunoabsorbant assay. The patients' mean venous tissue factor (235 +/- 101 pg/ml) and capillary tissue factor (268 +/- 106 pg/ml) were higher than those of the controls (161 +/- 42 pg/ml and 187 +/- 63 pg/ml, respectively, P < 0.05). These differences disappeared after adjusting for age. Capillary tissue factor levels were higher than venous tissue factor (244 +/- 102 pg/ml vs. 213 +/- 93 pg/ml), with a mean difference of 31 pg/ml (P = 0.0001). In addition, whole blood prothrombin time was lower in the capillary than in the venous samples (17.7 +/- 5 sec vs. 18.3 +/- 5.4 sec, P = 0.004). However, there was no correlation between capillary-venous differences in tissue factor and capillary-venous differences in the whole blood prothrombin time. Whole blood capillary and venous prothrombin times highly correlated with the plasma-based venous prothrombin time (r = 0.98, P < 0.0001). These results demonstrate that obtaining blood by fingerstick does not result in a clinically significant release of tissue factor. In addition, we did not observe any interference of plasma tissue factor with the whole blood prothrombin time assay. A direct relationship between tissue factor and age was observed.

Adult↗