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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↗
PubMed2002

[Prothrombin time and its standardization].

This review regarding prothrombin time and its standardization is described around some recent topics as the followings. 1. History of standardization for prothrombin time and revised WHO guideline for thromboplastin; A short history of standardization is summarized to understand a scheme of International Normalized Ratio (INR) based on International Sensitivity Index (ISI) that is calibrated by International Reference Preparation (IRP) for thromboplastin, and some key points in revised WHO guideline for thromboplastin and plasma used to control oral anticoagulant therapy are interpreted for research and practical use. 2. Point-of-care prothrombin time monitoring; A portable device to measure prothrombin time with whole blood sample, such as CoagChek (Roche), contributes to self-management by patients required long-term oral anticoagulation. Some investigators reported clinical agreement to use this monitoring system and improvement of patient's QOL and cost-effectiveness in overseas. 3. New types of thromboplastins; Two new types of thromboplastins have been available since the last year in Japan. One is a human plain thromboplastin, Simplastin HTF (Bioméreux) from extract of cultured human lung cancer cell, and another is IL test PT-Fibrinogen Recombinant (Iatron) from recombinant rabbit tissue factor relipidated in a synthetic phospholipid blend. For control of oral anticoagulation, good performance are expected in either thromboplastins because of their sufficient low ISI values. 4. INR methodology for other diseases; INR/ISI system is designed as a standardized methodology for control of oral anticoagulation. Prothrombin time, however is utilized as a global coagulation test for diagnosis or criteria of other disorders, such as congenital coagulation factor deficient, severe liver dysfunction and disseminated intravascular coagulation. Previous our study indicated that discrepancy of sensitivities to plasma absorbed multiple coagulation factors and plasma from patients under oral anticoagulation was revealed in rabbit brain thromboplastins, but not in human origins. Discrepancy of sensitivities observed in rabbit thromboplastins was emphasized in convert to INR values. These results suggested that the use of human thromboplastin of which ISI is close to 1.0 leads possibility for introducing INR methodology to evaluate PT of other disorders.

Environmental Monitoring↗
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↗
PubMed1998

Measurement of plasma fibrinogen concentration by the prothrombin-time-derived method: applicability and limitations.

A prothrombin-time-derived method was used to measure plasma fibrinogen concentration (PFC) in 286 samples from 242 normal and 44 orally anticoagulated subjects. Absorbance changes at 405 nm (deltaOD) during the clotting process were obtained by an automatic coagulometer and their relationship with plasma fibrinogen concentration (range 90-1090 mg/dl), measured by the Clauss method, was investigated. A weighted linear regression between the deltaOD and the Clauss-derived PFC values provided the best fit of the experimental data. The fitting equation was found to be reliable and accurate for PFC determination in normal subjects, whereas a systematic overestimate of fibrinogen level was demonstrated in plasma with high fibrinogen concentrations (> 400 mg/dl) and in plasma from anticoagulated patients. The systematic overestimate in the latter samples could be a result of an increased fibrin gel turbidity, as shown by in-vitro experiments using purified fibrinogen clotted by different thrombin concentrations. The PFC overestimate by the prothrombin-time-derived method could also be experimentally reproduced by competitively inhibiting thrombin-fibrinogen interaction by hirudin 54-65 peptide and the fibrinogen fragment E. A similar qualitative result was also found for the prothrombin-time-derived method in the presence of the Gly-Pro-Arg-Pro peptide, which competitively inhibits the end-to-end fibrin aggregation process. Notably, under both the above experimental conditions, the Clauss method underestimated the PFC. On the other hand, the 'clot recovery' method was minimally affected by the above inhibitors. These results indicate that the prothrombin-time-derived method is accurate and precise for most routine purposes. Its precision seems inadequate, however, under those conditions where the prothrombin time is prolonged (such as anticoagulant therapy) and in the presence of high fibrinogen levels.

Anticoagulants↗
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↗
PubMed1993

Comparison of native prothrombin antigen with the prothrombin time for monitoring oral anticoagulant prophylaxis.

BACKGROUND: Oral anticoagulation is most frequently monitored using the prothrombin time, but an alternative approach is measurement of native, fully carboxylated, prothrombin antigen (NPA). We have correlated results of the prothrombin time and NPA with development of venous thrombosis or bleeding complications in a clinical trial of warfarin prophylaxis following total hip arthroplasty to determine the potential value of NPA measurement for monitoring oral anticoagulation. METHODS AND RESULTS: Patients in one arm of a prospective, randomized trial received warfarin prophylactically beginning 10 to 14 days before total hip arthroplasty in a dose adjusted to prolong the international normalized ratio (INR) to 1.5 on the day of surgery and 2.5 after surgery. NPA was measured by ELISA, and the prothrombin time was measured using rabbit brain thromboplastin. Samples were tested from 97 patients, and data from 81 patients who had adequate venography were analyzed to correlate test results with occurrence of thrombosis. The prothrombin time and INR were less sensitive than NPA to the lowest intensities of anticoagulation, with the prothrombin time index increasing from 1.0 to 1.3 and the INR increasing from 1.0 to 2.0, whereas the NPA concentration decreased fourfold, from 200 to 50 micrograms/mL. There was little correlation between either the prothrombin time index or the INR and the development of thrombosis, whereas NPA concentrations were significantly higher on the day of surgery and on postoperative days 1, 3, 5, and 7 in patients who developed venous thrombosis. Higher concentrations of NPA were associated with an increased risk of venous thrombosis, but there was no relation between thrombosis and the prothrombin time index or INR. There was no significant correlation between surgical blood loss and prothrombin time index, INR, or NPA concentration. However, patients who received the largest number of transfusions on the day of surgery had significantly lower NPA concentrations than patients who required no transfusion. CONCLUSIONS: These results indicate that the NPA concentration more accurately reflects the antithrombotic effect of warfarin than does prothrombin time and may be superior in monitoring prophylactic oral anticoagulation.

Administration, Oral↗
PubMed2000

Stability of prothrombin time and activated partial thromboplastin time tests under different storage conditions.

Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are common laboratory tests that are useful in the diagnosis of coagulation disorders and monitoring anticoagulant therapy. Recent expansions in the outreach laboratory services at our institution prompted us to investigate the shipping limitations for some tests, including PT and aPTT. Although we followed NCCLS guidelines for the collection of blood specimens, we observed falsely elevated PT and aPTT values due to the different storage conditions. The objective of this study is to determine the effect of conditions and duration of storage on PT and aPTT tests using plasma and whole blood samples, respectively. For this study, 36 plasma samples with normal and prolonged PT and aPTT were exposed to different storage conditions. Blood was centrifuged immediately and plasma was stored at room temperature (RT), refrigerated at 4 degrees C, or frozen at -20 degrees C. The samples were analyzed at 0 h and repeated at 6, 12 and 24 h under various conditions. Although statistically significant differences were observed for plasma samples for normal PT tests after 12 h at refrigerated and frozen storage conditions, the differences would not change the clinical interpretation of the results. On the other hand, samples stored refrigerated or at RT showed significant differences for aPTT at 24 h. These differences would change clinical interpretation, especially for samples with normal or near normal aPTT times. Interestingly, aPTT was significantly higher for samples stored frozen when compared to refrigerated and RT conditions at 6 h. Similar patterns were also observed on ten whole blood samples with normal PT and aPTT values. In conclusion, either plasma or whole blood samples can be accepted for PT testing up to 24 h and for aPTT testing up to 12 h only, when transported either at RT or at 4 degrees C.

Humans↗
PubMed1985

Novel rhodamine tripeptide substrate for manual and automated colorimetric prothrombin time test.

A chromogenic prothrombin time test is described using the tripeptide substrate, (Sar-Pro-Arg)2-Rhodamine 110. The method is both precise and sensitive to the factors of the extrinsic pathway. The accuracy of the method was demonstrated by comparison of patient sample values to standard clotting test results. The manual substrate test was adapted to two different automated chemistry analyzers.

Autoanalysis↗
PubMed1991

Antibiotic treatment and associated prolonged prothrombin time.

The incidence and type of pathology causing a prolonged prothrombin time and clinical bleeding episodes were assessed in a multicentre study of 1109 patients receiving cefotetan, a N-methyl-thiotetrazole (NMTT), or equivalent antibiotics. There was no significant difference in the incidence of a prolonged prothrombin time (9.9% with cefotetan, 8.0% with comparable antibiotics) of clinical bleeding episodes. However, prothrombin time increases of greater than 12 seconds were significantly (p = 0.002) greater with cefotetan (3.8%) than with comparators (0.8%). In both antibiotic groups increases in prothrombin time were more likely following surgery and in patients who were older, with a high platelet count, low albumin, or higher urea and creatinine concentrations. All antibiotic treatment can be associated with prolonged prothrombin times and new agents should always be assessed in a large multicentre study before the practical, clinical importance of haemostatic defects can be defined.

Adolescent↗
PubMed1991

Effects of temperature and viscosity on prothrombin times of blood.

Accurate prothrombin time tests are important because they are frequently performed on presurgical patients to evaluate their blood-clotting status. We studied the effect of temperature (27-47 degrees C) on PTs obtained with eight different brands of thromboplastin. We also compared the sensitivities of two types of coagulation timers to changes in blood viscosities between 1 and 16 mPa/s. Viscosities were measured with the Brookfield Digital Viscometer. The MLA Eletra 800 and the BBL fibrometer were used to measure PTs. All eight thromboplastins gave convex curves of PT versus temperature, with optimum values lying between 38 and 39 degrees C. The curves were fitted to 4th-degree polynomials which showed that a mean temperature bias of 2 degrees C can increase PTs. Ortho Brain (7.8% change) was affected the most, while thromboplastin C (4.4% change) was affected the least. Plots of PT versus viscosity showed that the BBL fibrometer, which uses an electromechanical sensor, was more affected by viscosity than the MLA Electra 800, with an optical detector. However, above 8.2 mPa/s, all PTs were significantly elevated. Hence, patients with macroglobulinemia, whose plasma viscosities sometimes exceed 8.2 mPa/s, may have falsely elevated PTs. We conclude that temperature and viscosity are critical factors in the test and significantly contribute to within and between laboratory variations in PT measurements.

Blood Viscosity↗
PubMed2003

Potential dosing errors using portable prothrombin time monitoring devices.

Portable prothrombin time (PT) monitors facilitate the control of warfarin therapy. Few studies have compared the influence of using different monitors on dosage decisions. We determined the comparability of data generated by two portable PT monitors, Coaguchek S, (Roche Diagnostics Boehringer-Mannheim) and Hemochron Jr (International Technidyne Corporation Ltd.), with that of a reference laboratory. Simultaneous International Normalized Ratio (INR) measurements (portable monitor and laboratory) were performed in 193 consecutive patients receiving warfarin for at least 3 months. Agreement of measurements was assessed by both regression analysis and influence on dosage decisions in accordance with pre-defined criteria. The Coaguchek S versus laboratory INR regression line (n = 111; r2 = 0.88; P < 0.001) was close to the line of identity, while that of the Hemochron Jr (n = 82; r2 = 0.61; P < 0.001) was not. The overall proportion of dual INR measurements that fulfilled the clinical criteria of agreement was 90% for the Coaguchek S compared with 62% for the Hemochron Jr (P < 0.0001). For laboratory INRs 2.0-2.5, 2.6-4.0 and > 4.0, the proportions of portable measurements that satisfied the clinical criteria for the Coaguchek S versus the Hemochron Jr were 96 versus 63% (P < 0.001), 81 versus 45% (P < 0.04), and 67 versus 17% (P < 0.85), respectively. Warfarin dosing based solely on the portable devices would have resulted in unjustified dose increments in 22% of the patients with the Hemochron Jr device compared with 8% with the Coaguchek S monitor (chi2 = 4.43; P = 0.035). The Coaguchek S monitor provides measurements for INR values within the therapeutic range that agree well with the standard laboratory. The Hemochron Jr measurements result in different dosage adjustments even within the therapeutic range, but especially for INR values > 4.0. For both monitors, agreement of INR measurements with the standard decreases with increasing INR values.

Adult↗
PubMed1989

Cost effectiveness of monitoring warfarin therapy using standard versus capillary prothrombin times.

The authors assessed the cost effectiveness of monitoring warfarin therapy guided by standard plasma prothrombin times performed on blood samples obtained by venipuncture versus prothrombin times performed on capillary whole blood samples obtained by fingerstick. Twenty patients receiving long-term oral anticoagulation had either standard or capillary prothrombin times determined every other week for eight weeks in a cross-over design. All time intervals were monitored, including receptionist, secretarial, nursing, phlebotomy, etc., and costs for all materials, procedures, and labor were calculated. The total cost per test by the capillary whole blood prothrombin time method was significantly less than by standard prothrombin time methods ($7.55 vs. $15.64) even though the nurse-patient encounter time was greater per test for the capillary method (12.4 minutes vs. 8.3 minutes). The management of oral anticoagulation guided by prothrombin times performed on instrumentation designed to sample capillary whole blood should result in a significant cost savings, and because of the immediate availability of results, provide the potential for improved health care.

Administration, Oral↗
PubMed1992

Imprecision of prothrombin time monitoring of oral anticoagulation. A survey of hospital laboratories.

Prothrombin time monitoring of oral anticoagulation is highly dependent on the tissue thromboplastin used. In the United States, patients have received a higher level of anticoagulation because of the use of a less sensitive thromboplastin. Many advocate the use of an International Normalized Ratio to rectify this problem. Laboratory supervisors from all acute care hospitals in Massachusetts were surveyed to determine the disparity in thromboplastin use and reporting practices for prothrombin time testing. Eighty-eight of 103 (86%) hospitals responded. Fifty-eight lots from six manufacturers of thromboplastin were in use. The International Sensitivity Index of these lots ranged from 1.89 to 2.74. Ninety-nine percent of hospitals reported prothrombin times in raw seconds. Only 5% reported an International Normalized Ratio. Sixteen different coagulation instruments were in use. Close to 70% of laboratory supervisors had little or no understanding of the significance of an International Sensitivity Index or an International Normalized Ratio. The management of oral anticoagulation appears far less precise than had been believed. Prothrombin times in the same individual from different laboratories may have poor correlation. Based on the level of understanding of laboratory supervisors, extensive education will be necessary to change practices and improve accuracy and comparability of prothrombin time testing.

Administration, Oral↗
PubMed1993

Comparison of the behavior of normal factor IX and the factor IX Bm variant Hilo in the prothrombin time test using tissue factors from bovine, human, and rabbit sources.

A subset of hemophilia B patients have a prolonged bovine-brain prothrombin time. These CRM+ patients are classified as having hemophilia Bm. The prolongation of the prothrombin time has been reported only with bovine brain (referred to as ox brain in some literature) as the source of thromboplastin; prothrombin times determined with thromboplastin from rabbit brain or human brain are not reported to be prolonged. Factor IX from a hemophilia Bm patient (factor IX Hilo) was isolated. The activity of factor IX Hilo was compared to that of normal factor IX in prothrombin time assays when the thromboplastin source was of bovine, rabbit, or human origin. Factor IX, either normal or Hilo, prolonged a prothrombin time regardless of the tissue factor source. However, unless thromboplastin was from a bovine source, this prolongation required high concentrations of factor IX. Further, factor IX normal was as effective as factor IX Hilo in prolonging the prothrombin time when rabbit or human thromboplastin was used. With bovine thromboplastin, factor IX Hilo was significantly better than factor IX normal at prolonging the prothrombin time. The amount of prolongation was dependent on the amount of factor IX Hilo added. In addition, the prolongation was dependent on the concentration of factor X present in the sample. The prothrombin time changed as much as 20 seconds when the factor X concentration was varied from 50% to 150% to normal (fixed concentration of factor IX Hilo). These results demonstrate the difficulty of classifying the severity of a hemophilia Bm patient based on the bovine brain prothrombin time unless both the factor IX and factor X concentrations are known.

Animals↗
PubMedDate not supplied

Fat emulsion effects on prothrombin time in warfarin anticoagulated patients: an in vitro study.

The effect of lipid emulsions on prothrombin time in blood from anticoagulated patients was determined. Blood samples were obtained from 23 patients therapeutically anticoagulated with warfarin (prothrombin time 1.3-2.0 x control). Varying amounts of an intravenous lipid emulsion (Intra-lipid) were added to the blood to simulate concentrations seen in vivo with a constant lipid infusion. The prothrombin time was measured on the plasma from these samples and compared to the prothrombin time of the plasma samples without lipid. The mean decrease in prothrombin times were: 0.29 sec at 50 micrograms/ml, 0.23 sec at 100 micrograms/ml, and 0.29 sec at 200 micrograms/ml. All concentrations showed a statistically significant decrease (p less than 0.05) when compared to the control by the Scheffe test. Lipid emulsions appear to decrease the prothrombin times in anti-coagulated patients. The differences however, were small and not of clinical significance at the concentrations tested.

Fat Emulsions, Intravenous↗
PubMed1979

The varied sensitivity of partial thromboplastin and prothrombin time reagents in the demonstration of the lupus-like anticoagulant.

An acquired inhibitor of blood coagulation, similar to that described in patients with Systemic Lupus Erythematosus (SLE), was detected during routine coagulation screening in 10 patients who did not meet the criteria for a diagnosis of SLE. The lupus-like anticoagulant (LLAC) was diagnosed on the basis of prolonged activated partial thromboplastin time (APTT) and/or prothrombin time (PT) which failed to correct when patient plasma was added to normal plasma; an additional criterion was an abnormal tissue thromboplastin inhibition test. No patient had a specific inhibitor directed against factors VIII and IX. Demonstration of LLAC was highly dependent upon the type of reagents adopted in the APTT and PT: the abnormality was detected consistently by one reagent only. One-stage assays of factors VIII and IX were characteristic of the presence of an inhibitor, showing non-parellel dose-response curves or decreased activity at low dilutions which were partially corrected at higher dilutions. Although 7 patients were free of abnormal bleeding, unequivocal signs of haemorrhagic tendency after a surgery were present in the remaining 3 patients. The findings suggest that LLAC is a non-exceptional cause of prolonged coagulation screening tests, and that it may sometimes be associated with impaired haemostasis.

Adolescent↗