APPLICATIONS OF INTERNATIONAL RECOMMENDATIONS ON THE STANDARDIZATION OF PROTHROMBIN TIME IN ORAL ANTICOAGULANT CONTROL

1987 ◽  
Author(s):  
F Dati ◽  
U Becker ◽  
N Heimburger
Keyword(s):  
Prothrombin Time ◽  
Oral Anticoagulant ◽  
Calibration Procedure ◽  
Sensitivity Index ◽  
Chromogenic Substrate ◽  
Clotting Factors ◽  
Reference Preparation ◽  
Broad Variation ◽  
The Mean

The determination of prothrombin time (PT) in oral anticoagulant control is affected by a broad variation. The responsible factors are: type of thromboplastin incorporated in the PT reagents, procedure for use, clotting factors or heparin inhibitors added to the reagent, method of expression of PT results. Recently, joint recommendations have been issued by International Committees (ICSH/ICTH) taking into account the system of International Thromboplastins and the statistical model for thromboplastin calibration established by WHO. The aim is a standardization of commercial thromboplastins for PT tests in order to allow the use of the international scale of oral anticoagulant intensity (INR: Intern. Normalized Ratio). Following such recommendations we have standardized two new PT tests, based on coagulometric and photometric methods which rely on the same sensitive human placental thromboplastin. The coagulometric PT test (Thromborel®S) is performed with conventional coagulometers. The photometric PT assay (Chromoquick®) uses a new chromogenic substrate specific for thrombin. This method is based on the measurement of the time necessary to reach a fixed increase of absorbance (0.1 A) using a special microprocessor-controlled photometer.The two PT reagents were calibrated either directly against a reference preparation (BCT) or via an intermediate standard thromboplastin in two multicentric studies. The calibration procedure by the WHO method allows to assign the corresponding ISI (Intern. Sensitivity Index) to the PT reagent used and the transformation of the obtained prothrombin ratio (PR) into INR by the equation INR = PRISI. The calculated ISI values were 1.08 for the coagulometric PT reagent (n = 330) and 1.07 for the photometric reagent (n = 365), respectively.The reproducibility of the ISI value for the new human placental thromboplastin for 64 different batches amounts to 3.6 %, the mean ISI value being 1.12.Comparison with the reference thromboplastins in PR values gave a good correlation.A) Coagul. PT assay (x): r = 0.964; y = 1.03x ™ 0.1;B) Photom. PT assay (x): r = 0.940; y = 1.02x ™ 0.1.

Recombinant Tissue Factor as Substitute for Conventional Thromboplastin in the Prothrombin Time Test

1992 ◽  
Vol 67 (01) ◽  
pp. 042-045 ◽  
Author(s):  
Armando Tripodi ◽  
Arnaldo Arbini ◽  
Veena Chantarangkul ◽  
Pier Mannuccio Mannucci
Keyword(s):  
Prothrombin Time ◽  
Tissue Factor ◽  
Oral Anticoagulant Therapy ◽  
Clotting Factor ◽  
Rabbit Brain ◽  
Sensitivity Index ◽  
Clotting Factors ◽  
Wide Range ◽  
Reference Preparation ◽  
Time Test

SummaryRelipidated recombinant tissue factor (r-TF) has been assessed in comparison with conventional rabbit brain thromboplastin (Manchester Reagent) for its suitability for measurement of prothrombin time (PT). The International Sensitivity Index (ISI) of r-TF calibrated against the International Reference Preparation BCT/253 (human plain) was found to be 0.96 and 1.12 with instrumental and manual techniques. Our study of plasmas from patients with congenital deficiencies of clotting factors covering a wide range of severity demonstrates that r-TF is able to detect even minor deficiencies of factors involved in the extrinsic and common coagulation pathways. Patients with liver diseases were correctly diagnosed with a prevalence of abnormal results comparable for both reagents. Between-assay reproducibility expressed as coefficient of variation was 2.3 % and 3.9 % at normal and abnormal PT levels.In conclusion, our evaluation shows that relipidated r-TF possesses the necessary requisites of sensitivity, diagnostic accuracy and reproducibility which make it a suitable candidate for PT determination both for monitoring oral anticoagulant therapy and diagnosing congenital and acquired clotting factor deficiencies. Moreover, being a highly defined reagent it may constitute a step forward in the standardization of PT testing.

The Dependence of the International Sensitivity Index on the Coagulometer Used to Perform the Prothrombin Time

1990 ◽  
Vol 63 (03) ◽  
pp. 424-429 ◽  
Author(s):  
M J Ray ◽  
I R Smith
Keyword(s):  
Prothrombin Time ◽  
Reference Method ◽  
Calibration Procedure ◽  
World Health ◽  
Sensitivity Index ◽  
Optical Instruments ◽  
Different Types ◽  
Reference Preparation ◽  
Health Organization ◽  
International Sensitivity Index

SummaryThis study was designed to detect any effect that different types of coagulation instrument may have on the International Sensitivity Index (ISI) of a thromboplastin.Manufacturers of commercial thromboplastins now calibrate their reagents against the World Health Organization international reference preparation to assign them an IST. This enables the prothrombin time (PT) estimated with that reagent to be expressed as an International Normalised Ratio (INR).One batch of Thromborel S was calibrated against the Australasian Reference Thromboplastin (ART). The Thromborel S was used on three photo-optical instruments, the Automated Coagulation Laboratory (ACL) (Instrumentation Laboratory), the Cobas Fibro (Roche), and the Coag-a-Pet (General Diagnostics). PTs using ART were performed manually using the reference method.The ISIs calibrated in our laboratory when the ACL and Cobas Fibro were used were not significantly different at the 95% level, being 1.102 ± 0.018 and 1.134 ± 0.022 respectively. The ISI with the Coag-a-Pet of 1.223 ± 0.023 was significantly different to that of the ACL and the Cobas Fibro at the 95% level.The flowcharts for a computer program to perform the necessary calculations are provided. The program allows for the entry and editing of data from the calibration procedure, and provides a mean normal PT and normal range, the ISI and 95% confidence limits of the calibration, and a chart for the conversion of the test PTs to INRs.The authors have made available an IBM compatible program for the calibration of thromboplastins.

Multicenter Evaluation of a Chromogenic Substrate Method for Photometric Determination of Prothrombin Time

1987 ◽  
Vol 58 (03) ◽  
pp. 856-865 ◽  
Author(s):  
F Dati ◽  
M Barthels ◽  
J Conard ◽  
J Flückiger ◽  
A Girolami ◽  
...  
Keyword(s):  
Prothrombin Time ◽  
Anticoagulant Therapy ◽  
Photometric Determination ◽  
Coagulation Factors ◽  
Stable Phase ◽  
Photometric Method ◽  
Sensitivity Index ◽  
Chromogenic Substrate ◽  
Plasma Samples

SummaryA multicenter study of a chromogenic substrate method for photometric determination of prothrombin time was conducted in order to evaluate its clinical application. Seven laboratories pailicipaled in the study using a total of 742 plasma samples from 417 patients on oral anticoagulant therapy, 261 healthy subjects and 64 patients with different diseases especially of the liver as well as 30 patients with hereditary deficiency of coagulation factors II, V, VII, X. The chromogenic PT method was compared to a standardized coagulometric PT assay which uses the same sensitive human placenta thromboplastin calibrated against international reference preparations. A high correlation of the prothrombin ratio values of the chromogenic and the coagulometric assay was obtained in 402 plasma samples (r = 0.940; y = 1.02x − 0.1). The study showed that the chromogenic PT reagent is sensitive to deficiency of the coagulation factors of the extrinsic pathway but not affected by heparin up to 1 IU/ml because of the heparin antagonist added. The precision (coefficient of variation) of the photometric method ranged between 0.6 and 3% (intraassay CV) and between 1.4 and 5.8 (interassay CV). The International Sensitivity Index (ISI) obtained for the used lot was 1.09. The therapeutical range in percentage activity for patients in a stable phase of an anticoagulant therapy was found to be from 15 to 27 percent of normal. The results of the clinical evaluation proved the good comparability of the new chromogenic PT test with coagulometric methods, its high factor sensitivity, good reproducibility and easy performance.

scholarly journals European Concerted Action on Anticoagulation. Use of Plasma Samples to Derive International Sensitivity Index for Whole-Blood Prothrombin Time Monitors

2002 ◽  
Vol 48 (2) ◽  
pp. 255-260 ◽  
Author(s):  
Leon Poller ◽  
Michelle Keown ◽  
Nikhil Chauhan ◽  
Anton MHP van den Besselaar ◽  
Joyce Meeuwisse-Braun ◽  
...  
Keyword(s):  
Prothrombin Time ◽  
Whole Blood ◽  
Point Of Care ◽  
Chloride Concentration ◽  
Calibration Procedure ◽  
Sensitivity Index ◽  
Plasma Samples ◽  
Concerted Action ◽  
The Mean ◽  
International Sensitivity Index

Abstract Background: To simplify International Sensitivity Index (ISI) calibration, the possibility of substituting fresh plasma for fresh whole-blood samples with point-of-care testing (POCT) whole-blood monitors was investigated in a three-center study of three different POCT systems. Methods: A modified full WHO calibration procedure based on 20 healthy controls and 60 coumarin-treated patients was performed on three monitoring systems with whole-blood and plasma samples against plasma tested using the European Concerted Action on Anticoagulation (ECAA) rabbit reference plain thromboplastin and the manual prothrombin time (PT) method. Results: With one of the three systems, the mean ISI was 1.51 for whole blood and 1.49 for plasma; with the second system, the mean ISI was 1.08 for both whole blood and plasma. With the third system, however, the difference between the mean ISI for whole blood and that for plasma was greater (1.15 and 1.01, respectively). Overall, the precision of the calibrations was less than with traditional manual plasma PT testing. Conclusions: Provided that an appropriate calcium chloride concentration is used, the plasma PT results can be used for accurate ISI calibration of two of these three whole-blood POCT systems. Precision criteria need to be modified for POCT monitors.

THE RELIABILITY OF THE INTERNATIONAL NORMALISED RATIO (INR) DURING SHORT TERM ORAL ANTICOAGULANT TREATMENT

1987 ◽  
Author(s):  
A McKernan ◽  
J M Thomson ◽  
L Poller
Keyword(s):  
Induction Phase ◽  
Clotting Factors ◽  
Oral Anticoagulant Treatment ◽  
Sensitivity Indices ◽  
Freeze Dried ◽  
Wide Range ◽  
Reference Preparation ◽  
The Mean ◽  
The Individual ◽  
A Prospective Study

A prospective study has been performed to assess INR values obtained with a variety of thromboplastins during the early days of coumarin treatment. The reagents were BCT/253 (the primary International Reference Preparation), Diagen Activated, Diagen Freeze Dried, Manchester Reagent and Dade Thromboplastin FS. Prothrombin times were performed before the start of treatment and at regular intervals on fifteen patients who were given a slow induction regime. In theory INR should be the same irrespective of the thromboplastin. A wide range of values was however observed with the different thromboplastins on the same plasma samples. The mean deviations of the individual reagents from the mean INR obtained with the primary IRP were: Diagen Freeze-Dried 26%, Diagen Activated 13%, Dade FS 17%, Manchester Reagent 3%.There are two possible explanations for the discrepant findings. 1) In the induction phase Vitamin K dependent clotting factors are depressed at varying rates and thromboplastins differ in their sensitivity to the depression of these factors. The International Sensitivity Indices from which INR are derived are based on results from long-term stabilised patients. 2) The manufacturers' calibrations may be incorrect as demonstrated by the consistent differences of the results with some reagents from the IRP. The findings indicate therefore that INR values may not be dependable in the early days of oral anticoagulation with some thromboplastin reagents and that manufacturers' calibrations require independent assessment preferably by national control laboratories.

Multicenter Evaluation of Lyophilized and Deep-frozen Plasmas for Assignment of the International Normalized Ratio

1999 ◽  
Vol 82 (11) ◽  
pp. 1451-1455 ◽  
Author(s):  
L. L. Houbouyan-Reveillard ◽  
M. F. Aillaud ◽  
K. W. E. Denson ◽  
C. Droullé ◽  
M. Johnston ◽  
...  
Keyword(s):  
Prothrombin Time ◽  
External Quality Assessment ◽  
Calibration Procedure ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Local Calibration ◽  
External Quality ◽  
Different Types ◽  
Time Systems ◽  
International Sensitivity Index

SummaryThe interlaboratory variation of the International Normalized Ratio (INR) in various external quality assessment schemes is still relatively high. This is partly caused by inaccuracy of manufacturers’ stated International Sensitivity Index (ISI) and/or local instrumentation effects. The interlaboratory variation and accuracy of INR determinations may be improved by a local calibration procedure based on lyophilized plasmas with assigned INRs. The purpose of the present study was to determine INR values for different types of lyophilized plasmas to be used for local calibration. A total of 13 lyophilized plasmas (one normal, six from coumarin-treated patients, six artificially depleted) were analyzed by 10 laboratories, each using five calibrated prothrombin time (PT) systems. INRs were calculated for each plasma using each laboratory’s specific ISI and mean normal prothrombin time values. In the same way, five deep-frozen pooled plasmas from coumarin-treated patients were analyzed. There were significant INR differences for the lyophilized plasmas between the prothrombin time systems. The differences were relatively small for the deep-frozen coumarin plasmas (CV 2.6-3.3%) and three lyophilized coumarin plasmas from one manufacturer (CV 3.7-4.8%). Important INR differences were observed for three lyophilized coumarin plasmas from another manufacturer (CV 9.5-14.1%) and several artificially depleted plasmas (CV 5.3-12.8%). The citrate concentrations in the artificially depleted plasmas were lower than those in the normal and coumarin plasmas. These differences should be considered in the selection and certification of plasmas as calibrants for local calibration of PT systems. The lyophilized plasmas’ INR values obtained in the present study will be used for a field study of local PT calibration to assess their efficacy.

Thrombin Generation Is Normal in Most Patients with Cirrhosis despite a Prolonged INR.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1826-1826
Author(s):  
Alexander Gatt ◽  
Anne Riddell ◽  
Vincenza Calvaruso ◽  
Michael Makris ◽  
Edward Tuddenham ◽  
...  
Keyword(s):  
Liver Disease ◽  
Tissue Factor ◽  
Patient Group ◽  
Protein C ◽  
Thrombin Generation ◽  
Control Sample ◽  
Normal Subjects ◽  
Sensitivity Index ◽  
Clotting Factors ◽  
The Mean

Abstract Introduction: Advanced liver disease is associated with prolongation of the prothrombin time (PT). In order to decrease the inter-laboratory variability of PT measurement, the international normalised ratio (INR) calculated as the ratio of patient’s PT to a normal (control) sample, raised to the power of the international sensitivity index (ISI) of the particular thromboplastin used was developed. However, the ISI is derived from PT results of patients on warfarin and results cannot be extrapolated to liver patients. Despite this, the INR is still commonly performed to assess bleeding risk in patients with liver disease worldwide. Furthermore the INR is only affected by factors I, II, V, VII, and X and is not influenced by other factors such as factor VIII which is usually raised in hepatic cirrhosis. Recently it has been reportd that thrombomodulin addition (to take into account the protein C pathway) normalises thrombin generation (TG)1 despite these patients having a low TG if thrombomodulin is not used. Aim: We speculated that TG, which is a global assay of coagulation and sensitive to all coagulation factors, when triggered by a low tissue factor (TF) concentration might not correlate with the INR in patients with liver disease and that contact inhibition with corn trypsin inhibitor (CTI) might better reflect the coagulation potential in this patient group. Results: 73 unselected patients with liver cirrhosis due to various diseases and 25 normal subjects were studied. INR and TG using the calibrated automated thrombogram (CAT) at 1pM tissue factor (TF) with CTI, 5pM without CTI and with and without Protac (a Protein C activator) were performed using platelet poor plasma (PPP). The INR range was 0.8–4.0 (mean 1.6). At 5pM TF without Protac, the patient group had a significantly lower endogenous thrombin potential (ETP) than the controls (mean ETP difference 752nM/min; P <0.0001). With Protac, no significant differences could be detected between the 2 groups. However, if the ETP without Protac was divided by the ETP with Protac x 100, the liver group showed more resistance to PC activation (mean % difference 25.4; P 0.0002). At 1pM TF, the mean ETP in the cirrhosis cohort was slightly lower than the normal group (difference between means 216nM/min; P 0.03). However, only 7 (9.6%) patients had ETP values less than the normal range (mean±2SD). No correlation was found between the ETP at 1pM and the INR. The mean FVIII:C was raised at 185.6 (78–420U/dl). Conclusion: TG measured at low TF with CTI is normal in the majority of patients with cirrhosis. These patients are also more resistant to PC activation and have supranormal FVIII:C. Thus most patients have a normal or high thrombin potential despite an abnormal INR. These findings have important implications as in the absence of bleeding, “prophylactic” plasma and clotting factors are unnecessary.

Utility of a Modified Calibration Model for Reliable Conversion of Thromboplastin Times to International Normalized Ratios

1986 ◽  
Vol 56 (02) ◽  
pp. 178-182 ◽  
Author(s):  
G O Gogstad ◽  
J Wadt ◽  
P Smith ◽  
T Brynildsrud
Keyword(s):  
Anticoagulant Therapy ◽  
Coefficient Of Variation ◽  
Calculation Method ◽  
Oral Anticoagulant ◽  
Oral Anticoagulant Therapy ◽  
Calibration Model ◽  
Calibration Line ◽  
Modified Model ◽  
Reference Preparation ◽  
The Mean

SummaryThe combined thromboplastin reagent, Normotest, has been calibrated against the secondary international reference preparation for bovine thromboplastin, OBT/79. Three expert laboratories measured up to 62 patients on stabilized oral anticoagulant therapy and up to 20 normals in order to establish an INR-scale for Normotest. It was found that the model recommended by the WHO was less suited for the calibration of this thromboplastin. This is the first study in which three independent laboratories demonstrate a similar bias of the WHO calibration model. A modified model in which a correction factor is introduced was applied to the problem and proved to give a reliable calculation method for INR on Normotest. The mean coefficient of variation of INR calculated between measurements with Normotest and OBT/79 (scatter of data around calibration line) was 4.2-5.0% as compared to 5.1-5.7% for the WHO-method. A conversion scale for percent activities between Normotest and Thrombotest was established showing that the recommended therapeutic range of 5-10% Thrombotest (INR = 4.8-2.8) corresponds to 10-20% Normotest.

Reliability and Clinical Impact of the Normalization of the Prothrombin Times in Oral Anticoagulant Control

1985 ◽  
Vol 53 (01) ◽  
pp. 148-154 ◽  
Author(s):  
E A Loeliger ◽  
A M H P van den Besselaar ◽  
S M Lewis
Keyword(s):  
Oral Anticoagulant ◽  
International Normalized Ratio ◽  
World Health ◽  
Patient Specific ◽  
Sensitivity Index ◽  
Common Denominator ◽  
Reference Preparation ◽  
The Common ◽  
Health Organization ◽  
Low Sensitivity

SummaryIn 1983, the World Health Organization (WHO) published recommendations for normalization, in oral anticoagulant control, of the prothrombin time (PT). The common denominator is the International Sensitivity Index (ISI) of a thromboplastin, obtained by means of thromboplastin calibration. The common scale is that of the International Normalized Ratio (INR). The INR is the PT ratio Patient PT/normal PT which would have been found normal PT with the WHO primary international reference preparation (IRP) 67/40. The reliability of the INR depends on the extent of calibration precision, patient-specific influences, as well as interlaboratory variation in the PT determination. Under well-controlled conditions the overall coefficient of variation (CV) of the INR is 11-13.5%, if thromboplastins of ISI ≃ 1 are used. For so-called low-sensitivity thromboplastins (ISI ≃ 2-2.5), the overall variation is larger due to a large between-laboratory variation of the measured PT-ratiosThe user of thromboplastin will be provided with a chart or graph enabling him to convert the conventional terms used for expressing PTs into INRs. For quality assurance, and to prepare his own calibration chart if necessary, he should check normalization by means of control plasmas to which INRs have been assigned.There is sufficient clinical evidence to express optimal therapeutic ranges in terms of INR. Manufacturers should revise and adapt their inserts where necessary in order to conform to these requirements.

Comparison of a New Automated Amidolytic Assay of Thrombin Generation with “ Prothrombin Time” and “Thrombotest”.

1979 ◽  
Author(s):  
J.J.C. Jonker ◽  
L.H.M. van Riel ◽  
M.M.P. Paulssen
Keyword(s):  
Prothrombin Time ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Chromogenic Substrate ◽  
Automated Method

An automated method was developed for the determination of thrombin generation in citrated whole blood during activation by thromboplastin. The thrombin generated was allowed to split the chromogenic substrate Tos-Gly-Pro-Arg-pNA yielding p-Nitroaniline. The comparison with this method and “Prothrombin time” in 50 samples was significant (r = 0,88 P < 0,001) and also in 503 samples with “Thrombotest” (r = 0,73 P < 0,001). This assay may serve as a specific, precise and fast and cheaper alternative for “prothrombin time” and “Thrombotest” in large Thrombosis Services.

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