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

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.

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Outcomes of Oral Anticoagulant Therapy Managed by Telephone vs In-Office Visits in an Anticoagulation Clinic Setting

Yearbook of Pulmonary Disease ◽

10.1016/s8756-3452(08)70664-9 ◽

2008 ◽

Vol 2008 ◽

pp. 219-220 ◽

Cited By ~ 1

Author(s):

K.L. Lewis

Keyword(s):

Anticoagulant Therapy ◽

Oral Anticoagulant ◽

Oral Anticoagulant Therapy ◽

Anticoagulation Clinic ◽

Office Visits ◽

Clinic Setting

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Confusion Over the Therapeutic Range for Monitoring Oral Anticoagulant Therapy in North America

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642740 ◽

1988 ◽

Vol 59 (02) ◽

pp. 129-132 ◽

Cited By ~ 24

Author(s):

J Hirsh ◽

M Levine

Keyword(s):

North America ◽

Anticoagulant Therapy ◽

Therapeutic Range ◽

Oral Anticoagulant ◽

Oral Anticoagulant Therapy

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Controlled Trial of the Sequential Use of Streptokinase and Ancrod in the Treatment of Deep Vein Thrombosis of Lower Limb

Thrombosis and Haemostasis ◽

10.1055/s-0038-1649223 ◽

1977 ◽

Vol 37 (02) ◽

pp. 222-232 ◽

Cited By ~ 12

Author(s):

D. A Tibbutt ◽

C. N Chesterman ◽

E. W Williams ◽

T Faulkner ◽

A. A Sharp

Keyword(s):

Deep Vein Thrombosis ◽

Clinical Improvement ◽

Anticoagulant Therapy ◽

Lower Limb ◽

Oral Anticoagulant ◽

Controlled Trial ◽

Oral Anticoagulant Therapy ◽

Control Group ◽

Vein Thrombosis ◽

Deep Vein

SummaryTreatment with streptokinase (‘Kabikinase’) was given to 26 patients with venographically confirmed deep vein thrombosis extending into the popliteal vein or above. Treatment was continued for 4 days and the patients were allocated randomly to oral anticoagulant therapy or a course of treatment with ancrod (‘Arvin’) for 6 days followed by oral anticoagulant therapy. The degree of thrombolysis as judged by further venographic examination at 10 days was not significantly different between the 2 groups. The majority of patients showed clinical improvement but there was no appreciable difference between the groups at 3 and 6 months. Haemorrhagic complications were a more serious problem during the period of treatment with ancrod than during the equivalent period in the control group.

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Relationship Between Total Prothrombin, Native Prothrombin and the International Normalized Ratio (INR)

Thrombosis and Haemostasis ◽

10.1055/s-0038-1656342 ◽

1992 ◽

Vol 68 (02) ◽

pp. 160-164 ◽

Cited By ~ 3

Author(s):

P J Braun ◽

K M Szewczyk

Keyword(s):

Anticoagulant Therapy ◽

Oral Anticoagulant ◽

Inverse Relationship ◽

Low Dose ◽

Oral Anticoagulant Therapy ◽

International Normalized Ratio ◽

Antigen Assay ◽

Dose Oral ◽

Anticoagulated Patients ◽

Sensitive Method

SummaryPlasma levels of total prothrombin and fully-carboxylated (native) prothrombin were compared with results of prothrombin time (PT) assays for patients undergoing oral anticoagulant therapy. Mean concentrations of total and native prothrombin in non-anticoagulated patients were 119 ± 13 µg/ml and 118 ± 22 µg/ml, respectively. In anticoagulated patients, INR values ranged as high as 9, and levels of total prothrombin and native prothrombin decreased with increasing INR to minimum values of 40 µg/ml and 5 µg/ml, respectively. Des-carboxy-prothrombin increased with INR, to a maximum of 60 µg/ml. The strongest correlation was observed between native prothrombin and the reciprocal of the INR (1/INR) (r = 0.89, slope = 122 µg/ml, n = 200). These results indicated that native prothrombin varied over a wider range and was more closely related to INR values than either total or des-carboxy-prothrombin. Levels of native prothrombin were decreased 2-fold from normal levels at INR = 2, indicating that the native prothrombin antigen assay may be a sensitive method for monitoring low-dose oral anticoagulant therapy. The inverse relationship between concentration of native prothrombin and INR may help in identification of appropriate therapeutic ranges for oral anticoagulant therapy.

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Determination of the International Sensitivity Index of a New Near-Patient Testing Device to Monitor Oral Anticoagulant Therapy

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657641 ◽

1997 ◽

Vol 78 (02) ◽

pp. 855-858 ◽

Cited By ~ 25

Author(s):

Armando Tripodi ◽

Veena Chantarangkul ◽

Marigrazia Clerici ◽

Barbara Negri ◽

Pier Mannuccio Mannucci

Keyword(s):

Linear Relationship ◽

Whole Blood ◽

Oral Anticoagulant ◽

Oral Anticoagulant Therapy ◽

Oral Anticoagulants ◽

Calibration Model ◽

Testing Device ◽

Data Points ◽

Near Patient Testing

SummaryA key issue for the reliable use of new devices for the laboratory control of oral anticoagulant therapy with the INR is their conformity to the calibration model. In the past, their adequacy has mostly been assessed empirically without reference to the calibration model and the use of International Reference Preparations (IRP) for thromboplastin. In this study we reviewed the requirements to be fulfilled and applied them to the calibration of a new near-patient testing device (TAS, Cardiovascular Diagnostics) which uses thromboplastin-containing test cards for determination of the INR. On each of 10 working days citrat- ed whole blood and plasma samples were obtained from 2 healthy subjects and 6 patients on oral anticoagulants. PT testing on whole blood and plasma was done with the TAS and parallel testing for plasma by the manual technique with the IRP CRM 149S. Conformity to the calibration model was judged satisfactory if the following requirements were met: (i) there was a linear relationship between paired log-PTs (TAS vs CRM 149S); (ii) the regression line drawn through patients data points, passed through those of normals; (iii) the precision of the calibration expressed as the CV of the slope was <3%. A good linear relationship was observed for calibration plots for plasma and whole blood (r = 0.98). Regression lines drawn through patients data points, passed through those of normals. The CVs of the slope were in both cases 2.2% and the ISIs were 0.965 and 1.000 for whole blood and plasma. In conclusion, our study shows that near-patient testing devices can be considered reliable tools to measure INR in patients on oral anticoagulants and provides guidelines for their evaluation.

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