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PubMedDate not supplied

The effect of instruments for prothrombin time testing on the international normalized ratio.

Prothrombin time (PT) testing is used for monitoring oral anticoagulant therapy, its result being usually expressed as international normalized ratio (INR). This is done using the international sensitivity index (ISI) specific of thromboplastin employed to carry out the test. In this way a good PT standardization may be achieved although the instruments used to calibrate the thromboplastins might influence the ISI value.

Administration, Oral↗
PubMed1990

Prothrombin time in the monitoring of oral anticoagulant: a comparison of results using different thromboplastins.

The objective of this report is to compare the prothrombin time performed with thromboplastin of different tissues and species in patients under oral anticoagulant therapy as well as the way of expressing the results. The results showed that the ISI of the thromboplastin of human and rabbit brain are very close to the IRP BCT/253 (1.2 vs 1.1) and RBT/79 (1.3 vs 1.4), respectively. In contrast, the rabbit lung thromboplastin showed the greatest differences in the ISI values (1.6 vs 1.4) and in the CV (6.1%). The authors found significant statistical differences with the results of the prothrombin time as expressed in activity percentage (p less than 0.001) in three plasma pools of patients under different oral anticoagulant level for all thromboplastins studied. However, if the results are expressed in terms of INR, the values obtained are almost the same. The results here reported would demonstrate that the prothrombin time as INR allows the use of only one scheme for oral anticoagulant control when the thromboplastin reagent is calibrated according to the recommendations of the WHO.

Administration, Oral↗
PubMed1981

Chromogenic substrate (S-2222) factor X assays in the follow-up of coumarin treated patients. No advantage over prothrombin time and/or thrombotest.

Factor X was assayed in 30 patients on long-term anticoagulation by means of a chromogenic substrate (S-2222) for a total of 120 determinations. The average level found was 25.38 +/- 9.38% of normal. A satisfactory correlation was found between the factor X chromogenic level and the prothrombin time or Thrombotest percental values. However, factor X levels as determined by the chromogenic assay were usually higher than the global tests percental figures. The factor X chromogenic level was also slightly higher than the RVV-cephalin factor X assay. Since the chromogenic assay does not allow any new information to be made on the coumarin induced defect and since the costs of the assay are about 20-30 times higher than those of a simple prothrombin time, the test seems to play no part in the follow-up of coumarin therapy.

Blood Coagulation Tests↗
PubMed1994

Prolongation of the prothrombin time after organophosphate poisoning.

Prolongation of the prothrombin time owing to a transient reduction in factor VII activity is described in a 14-month-old child with organophosphate poisoning. Correction after vitamin K administration suggested an organophosphate-related effect on vitamin K-dependent factor VII activity. Historically, coagulation screening has not been routinely recommended after organophosphate intoxications. We suggest, however, that routine screening in such patients may be important. A brief review of organophosphate poisoning and the unique features of our case are presented.

Acetylcholinesterase↗
PubMed1995

A simple method for the derivation of the international normalized ratio for the reporting of prothrombin time results.

In order to harmonize the prothrombin time (PT) reporting systems, the World Health Organization, in collaboration with the International Committee on Thrombosis and Hemostasis, and the International Council on the Standardization in Hematology proposed a reporting system, the so-called international normalized ratio (INR). As the calculation of the INR depends on mathematical formula requiring a special calculator or mathematic tables, its derivation is associated with some difficulties and errors. In this article a nomogram is presented, by which derivation of the INR from different PT reporting methods can be easily done within a few seconds.

Anticoagulants↗
PubMed1991

Routine prothrombin time determination before elective gynecologic operations.

The prothrombin time (PT) test is routinely ordered to identify unsuspected bleeding disorders in patients before elective operations. We evaluated the usefulness of screening PT tests before elective gynecologic operations over a 6-month period at Women's Hospital in Los Angeles, California. Of 1546 patients, 1516 (98.1%) had normal test results. Charts of 25 of the 30 patients with abnormal values were available for review: 20 did not benefit from the test results, and five had indications for coagulation testing on history or physical examination. In the absence of specific indications, routine preoperative PT testing before elective gynecologic operations does not contribute to patient care and should be eliminated.

Anticoagulants↗
PubMed1988

A simple nomogram for the derivation of international normalised ratios for the standardisation of prothrombin times.

The WHO international scale of reporting prothrombin time results is based on the calibration of local and commercial thromboplastin reagents used in the test against an international reference preparation to derive an International Sensitivity Index (ISI) for each batch of local reagent. This quantifies an individual reagent's responsiveness to the coumarin induced defect. Once the ISI has been assigned, the derivation of International Normalised Ratios (INR) for reporting results depends on the use of a scientific calculator by which the local ratio is raised to the power of the ISI of the local reagent or use of an alternative formula and logarithms. A system for interpretation of INR, without the need for calculations, is presented for the known range of thromboplastins between 1.0 and 3.0 ISI in nomogram form. This chart may facilitate the general application of the INR system.

Humans↗
PubMed1982

Cold-induced contact surface activation of the prothrombin time in whole blood.

Studies of the prothrombin time (PT) have revealed that contact with borosilicate or commercial siliconized borosilicate markedly shortens the PT. This shortening is related to the activation of the contact phase of blood coagulation. This shortening of the PT occurs in both normal whole blood and plasma when stored in borosilicate or siliconized borosilicate tubes at 4 degree C and to a lesser degree at room temperature. Studies indicated the importance of several coagulation factors in decreasing the PT. The PT did not change in blood deficient in factor XII or in plasma deficient in Fletcher factor or high molecular weight kininogen, while blood deficient in CI esterase inhibitor (CI INH) had the most profound shortening. Shortening of the PT correlated directly with increased levels of factor VII. When purified CI INH was added to normal blood, it markedly reduced the activation of factor VII and the shortening of the PT in a dose-related manner. These studies indicate the pivotal roles of the contact phase of coagulation in initiating activation of the PT and of CI INH in inhibiting the activation of the coagulation factor(s) responsible for the cold-promoted activation of factor VII.

Blood Coagulation Factors↗
PubMed2003

Therapeutic concordance of two portable monitors and two routine automatic oral anticoagulant monitoring systems using as reference the manual prothrombin time technique.

Two models of capillary blood prothrombin time (PT) monitoring systems were evaluated for analytical performance and then compared with two routine PT systems using the reference manual technique and a high-sensitivity thromboplastin. Two sets of 60 and 80 plasmas were analyzed from anticoagulated patients stabilized over 3 months in an INR range 2-3.5 for therapy. Capillary PT determination was performed in two portable monitors, CoaguChek S and CoaguChek PT (Roche Diagnostics), and plasma automatic methods were Neoplastine/STA (Diagnostics Stago) and PT-FibrinogenHsPlus/ACL7000 (Instrumental Laboratories). Thromboplastin Bilbao (TBi), an in-house high-sensitivity rabbit thromboplastin (ISI=1.08), recommended as the reference reagent by an External Spanish Oral Anticoagulant Quality Assessment, was used in the PT manual technique. The two monitors' coefficients of correlation with the reference system were 0.74 for CoaguChek S and 0.81 for CoaguChek PT. The automatic routine systems showed a correlation of 0.92 (Neoplastine/STA) and 0.91 (PT-FbHsPlus/ACL7000). Clinical agreement expressed as the percentage of simple correlation ranged between 75.0% (CoaguChek S) and 88.9% (Neoplastine/STA). The systems having the best kappa index with the manual technique were CoaguChek PT (71.9%) and the Neoplastine/STA system (73%). The routine PT management systems exhibited better correlation and percentage of concordance when using the TBi/manual technique than did the portable monitors, which moreover performed unequally in this regard.

Anticoagulants↗
PubMed1986

Turbidimetric determination of prothrombin time by clotting in a centrifugal analyzer.

Two thromboplastin reagents ("Thrombotest" and "Normotest Automated") were used in evaluation of an automated method for determination of prothrombin time based on turbidimetric measurement of clot formation in a centrifugal analyzer. We used 60 plasma samples from patients with various diseases or being treated with oral anticoagulant and 16 normal plasma samples. Prothrombin times were calculated by a computer connected to the analyzer, a reading being made at either a certain per cent increase in total absorbance or a fixed absorbance increase. Both correlated well with the manual method (r = 0.98-0.99). The reading points best fitting the manually obtained data were estimated by minimizing the residual sum of squares in regression analyses performed at various absorbance increases. The per cent reading was better in this respect. Normotest Automated could be nearly perfectly related to the manual method, whereas Thrombotest showed a (negligibly) small deviation. Reproducibility was good within run (CV less than or equal to 3.2%) as well as between batch of the reagents, as assessed from variation in INR (CV less than or equal to 4.9%). We conclude that turbidimetry of clot formation may be validly used in automation of the prothrombin-time test. The equipment needed and the total time per analysis are about as for chromogenic substrate methods, but reagent cost is considerably lower.

Anticoagulants↗
PubMed1989

Prothrombin time ratio and other factors associated with bleeding in patients treated with warfarin.

We previously showed that the risk of major hemorrhage in patients with venous thromboembolism treated with warfarin was strongly related to duration of anticoagulant therapy. We here report the results of a more detailed analysis of factors other than duration of warfarin therapy associated with the risk of hemorrhage in these patients. Almost 7% of patients had a major hemorrhage on warfarin and an additional 23.7% had at least one minor bleeding episode. Age, female sex, and congestive heart failure were associated with small increases in the risk of major hemorrhage but not with the risk of minor bleeding. A prothrombin time ratio greater than 2.5 was associated with a fourteen-fold increase in the risk of a major hemorrhage (95% CI 5.1, 42.7), but major hemorrhages occurred in patients on warfarin at all measured values of the prothrombin time ratio. Taken together with the findings from our previous analysis, the study suggests that prevention of bleeding in patients on warfarin would best be accomplished by minimizing the duration of warfarin therapy, by scrupulous monitoring of the prothrombin time ratio, and by considering the "therapeutic range" for the prothrombin time ratio to be somewhat less than 2.0-2.5.

Adult↗
PubMed1999

Variability of prothrombin time and activated partial thromboplastin time in the diagnosis of increased surgical bleeding.

BACKGROUND: Prothrombin time (PT) and activated partial thromboplastin time (APTT) are used to diagnose causes of increased surgical bleeding and to guide treatment of acquired coagulation factor deficiency. This study compared the sensitivity of various commercial PT and APTT tests in patients with dilutional coagulopathy. STUDY DESIGN AND METHODS: A prospective study was used to identify patients who experienced increased surgical bleeding during elective extensive (>10 spinal segments) spinal fusion and instrumentation. In patients with clinical signs of increased bleeding, blood was obtained to compare the sensitivity of various commercial PT and APTT tests. PT, PT ratio, the International Normalized Ratio (INR), APTT, and APTT ratio were compared for their sensitivity in the diagnosis of a dilutional coagulopathy. RESULTS: Sixteen patients experienced increased bleeding during surgery. Mean estimated blood volume lost exceeded 1 blood volume (1.14 +/- 0.28). PT and APTT test results varied markedly. In the most sensitive PT and APTT tests, the results were 1.5 times the mean reference range values in all but on of the patients. The least sensitive combination of tests had results that were 1.5 times the mean reference range values in only 2 of 16 patients. Variability among tests was not reduced by the use of the PT or the APTT ratio, by the use of INR, or by incorporation of a measure of PT or APTT test sensitivity to factor-deficient serum. CONCLUSION: In surgical patients with dilutional coagulopathy, diagnostic and treatment decisions could depend on which PT and APTT test was used to determine the etiology of increased bleeding. This study indicates that the relationship between increased bleeding and an increased PT and APTT may be more difficult to define than is suggested by current practice guidelines. Each laboratory must establish guidelines based on reagent and instrument sensitivity to coagulation factor dilution.

Blood Coagulation Disorders↗
PubMed1998

A cross-Canada survey of prothrombin time testing: Does the establishment of local ISI values improve the accuracy of international normalized ratio reporting? Thrombosis Interest Group of Canada.

The international normalized ratio (INR) was established as a means of standardizing the prothrombin time regardless of the thromboplastin used in the individual laboratories. The INR is the prothrombin time ratio of the sample raised to the power of the International Sensitivity Index (ISI). Traditionally, the ISI is determined by using a manual clotting technique by comparing the test thromboplastin with a World Health Organization international reference thromboplastin with results from 60 patient samples standardized on warfarin, and 20 samples from normal volunteers. Most laboratories no longer perform prothrombin time testing by a manual technique but instead automate the procedure by using a variety of coagulation instruments. Thromboplastin ISI values have the potential to be modified considerably by instrumentation, and as a consequence, they, may result in INRs that are unreliable when compared to those obtained by the traditional manual method. It has been proposed that the use of calibrant plasmas tested with the laboratory's thromboplastin and instrument may overcome this problem and a local ISI value could be established. Our study objective was to determine whether a local ISI calibration with the plasma calibrants could reduce the variation of the INR over a wide range of thromboplastin/ instrument combinations. A total of 58 laboratories from across Canada, including community hospitals, private laboratories, and large tertiary care units, participated. The findings indicate that the use of calibrant plasmas to calculate the local ISI does improve the accuracy of INR reporting in the majority of thromboplastin/instrument combinations.

Autoanalysis↗
PubMed2004

A simple combination of serum type IV collagen and prothrombin time to diagnose cirrhosis in patients with chronic active hepatitis C.

BACKGROUND/AIM:: Cirrhosis in chronic hepatitis C is a major cause of mortality. The components of reported diagnostic indices of cirrhosis based on biochemical markers may be modified by therapies for hepatic inflammation. We aimed to construct index of cirrhosis in patients treated for chronic active hepatitis. METHODS:: Using sera of consecutive 140 patients with chronic hepatitis C, routine blood tests including fibrosis markers, type IV collagen and procollagen type III peptide (PIIIP), were performed. Diagnosis of cirrhosis was determined by biopsy. Using multivariate analyses, diagnostic indices of cirrhosis were constructed. RESULTS:: Fifty-eight patients were diagnosed to have cirrhosis. Platelet count, prothrombin time, and albumin were lower, and type IV collagen and PIIIP were higher in patients with cirrhosis (p<0.05). There was no difference in aspartate and alanine aminotransferases (AST, ALT) and gamma-glutamyl-transpeptidase (GGT) (p>0.3). Our diagnostic indices I (prothrombin time and platelet count) and II (prothrombin time and type IV collagen) of cirrhosis showed the area under the ROC curves (AUC) of 0.77 and 0.81, respectively. The index II was relatively superior to the index I. CONCLUSIONS:: Using combination of type IV collagen and prothrombin time, efficient diagnosis of cirrhosis can be performed in patients with chronic active hepatitis C.

Journal Article↗
PubMedDate not supplied

Comparative study of a portable monitor for prothrombin time determination, Coaguchek, with three systems for control of oral anticoagulant treatment.

Self-testing of oral anticoagulation is a new possibility related to the development of portable capillary whole blood prothrombin time monitors. The aim of this study was to evaluate one of this monitors, Coaguchek, with respect to its comparability with our routine prothrombin time determination system, as well as with the reference manual technique and two thromboplastins of high sensitivity, Manchester Reagent and one manufactured in our center, Thromboplastin Bilbao, in a group of patients on oral anticoagulant treatment. Although a correlation of r = 0.9271 was found between international normalized ratio (INR) values of Coaguchek and our routine method, Neoplastine/STA analyzer, the difference of the INR scatter increased with the magnitude of measurement, being lowest for INR between the portable monitor and Manchester Reagent and Thromboplastin Bilbao, with a similar coefficient of correlation, r = 0.8948 and r = 0.8905, respectively. A test was performed showing a 65.6% agreement with the INR values of the STA analyzer, 66.4% with Manchester Reagent and 73.4% with Thromboplastin Bilbao. On the basis of this correspondence with laboratory prothrombin time results Coaguchek may be considered as a possible option for monitoring anticoagulated patients even though patients should be given instructions and advice as regards the management and interpretation of the results.

Administration, Oral↗
PubMed2001

Accuracy and precision of point-of-care testing for glucose and prothrombin time at the critical care units.

The use of point-of-care testing (POCT) in critical care patient units has continued to increase since the 1980s. This increase is due to the need for prompt therapeutic interventions that may impact mortality and morbidity, and reduce the overall cost of healthcare for critically ill patients. The diagnostic manufacturing industry has risen to this challenge by introducing portable and/or handheld analyzers for use at the point-of-care. In order to ensure the public safety in the USA, the Food and Drug Administration (FDA) must approve the use of each POCT analyzer. The FDA approval is based on established performance criteria that includes relative accuracy and precision documentation. This study evaluated the precision and accuracy of the POCT prothrombin time and glucose analyzers relative to the manufacturers' specifications, to the internal QC in the main laboratory, and to the results of the external proficiency-testing program. The QC for the prothrombin time had a precision that ranged from 2.84% to 3.45% (POCT) and from 1.27-1.66% (main laboratory). The precision for the glucose QC ranged from 5% to 5.2% (POCT) and 0.9-2.7% (main laboratory). Using the results of the external proficiency testing, the inter-laboratory CV% for the POCT prothrombin time ranged from 3.5% to 5.0% and the main laboratory had a range of 2.5-2.9%. The inter-laboratory CV% ranges for glucose POCT and the main laboratory were 4.9-10.6% and 1.8-3.5%, respectively. The main laboratory analyzers proved to be more accurate than the POCT analyzers as indicated by comparison to the mean prothrombin time and glucose results of all participating laboratories in the proficiency testing program.

Blood Glucose↗
PubMed2001

[The factors that influence the consistency of international normalized ratio of prothrombin time].

OBJECTIVE: To investigate the factors that influence the consistency of international normalized ratio (INR) of prothrombin time. METHODS: Using the same automated blood coagulation analyzer and INR calibration plasma with two different types of prothrombin time (PT) reagent to assay the INR values of 19 controls (group 1), 12 patients who took long-term anticoagulant orally (group 2), 12 patients who took it at the first time (group 3) and 8 patients who took long-term anticoagulant together with cephalosporin N (group 4). RESULTS: The two kinds of reagents gave quite different INR values in all four groups (P < 0.01). The INR difference in group 3 (0.23 +/- 0.07, n = 12) was larger than that in group 2 (0.51 +/- 0.20, n = 12) (P < 0.01). The difference in group 4 (0.61 +/- 0.21, n = 8) was larger than that in group 2 (P < 0.01). CONCLUSIONS: The factors that may influence INR consistency are the source and sensitivity of the reagents, as well as the period of the anti coagulant been taken and the other drugs taken at the same time.

Administration, Oral↗
PubMed2003

Sensitivity of different prothrombin time assays to factor VII deficiency in canine plasma.

The factor VII sensitivity of prothrombin time (PT) in dogs was tested using five different PT reagents and a commercial PT variant. The five PT reagents were used according to manufacturers' instructions (standard test, PT([ST])) and also using a modified test instruction (modified test, PT([MT])). Plasma samples with defined factor VII levels (10-100%) were prepared by adding increasing quantities of canine factor VII deficient plasma to the pooled plasma of healthy dogs. Statistical comparison based on prothrombin time ratios (PTR = PT sample: PT measured for 100% factor VII activity level) revealed significant differences between different reagents for PT([ST]) and also for PT([MT]). Factor VII activity at which PT was prolonged to the upper limit of the reference values (FVII([X(0.975)])) was 16-39% (PT([ST])) and 23-35% (PT([MT])). Factor VII sensitivity measured by PTR and also by FVII([X(0.975)]) values, was higher in four of five PT reagents using PT([MT]) when compared with PT([ST]). The results of this study indicate the importance of selecting a sensitive reagent and method for PT measurement and for careful interpretation of PT test results using canine plasma.

Animals↗