Multicentric Evaluation of a New PT Reagent Based on Recombinant Human Tissue Factor and Synthetic Phospholipids

Precision is defined as the agreement between replicate analyses of the same material. Within-laboratory precision of the prothrombin time (PT) and INR can be optimized by choosing an appropriate combination of thromboplastin and instrument. Accuracy (true value) of the International Sensitivity Index (ISI), required for the calculation of INR, depends on the choice of international reference preparation for the thromboplastin, and on the instrument used by the local laboratory. Interaction between thromboplastin and each patient’s individual coagulation factors influences the accuracy of the INR. The contributions of imprecision, inaccuracy, and interaction effects can be combined to calculate the total uncertainty of the INR using Tomenson’s equation. Confidence intervals for the INR were calculated in typical examples. The 95% confidence intervals of the INR around 3 are approximately as wide as currently recommended therapeutic target ranges.

Section: Precision Of Isisupporting

confidence: 66%

Precision And Accuracy Of The International Normalized Ratio In Oral Anticoagulant Control

Besselaar

1996

“…Clearly tissue factor molecules in thromboplastins derived from different animal species, including recombinant tissue factor, are unlikely to behave identically [20,21]. Both the affinities and the changes in the FVII that result from its binding to different tissue factor molecules undoubtedly contribute to the differences that are observed.…”

Section: Inconsistency In Inr Values For Single Patient Samples Measumentioning

confidence: 99%

A Critical Evaluation of the Prothrombin Time for Monitoring Oral Anticoagulant Therapy

Jackson¹,

Esnouf

Lindahl

2003

The Quick prothrombin time is the most common clotting test performed, principally for monitoring oral anticoagulant therapy. The International Normalized Ratio (INR) for comparing patient results from prothrombin time measurements and the International Standardized Index (ISI) for achieving greater consistency of results using different thromboplastins have made it possible to compare the results of vitamin K antagonist drug therapy that was impossible before the introduction of the INR and ISI. However, INR values obtained from the same patient plasma sample using different thromboplastins are significantly different. This is so even when the thromboplastins have nearly the same ISI values. We suggest that investigation of patient-specific differences can provide a means by which the INR discrepancies can be identified and understood and thus lead to better methods for monitoring oral anticoagulant therapy.

“…The influence of heparin on the PT Innovin was already investigated in vitro [4], The PT Innovin was hardly affected by heparin up to a plasma concentration of 3 U/ml. Our data obtained in samples from patients on heparin confirm that the PT Inno vin is less influenced by the presence of hepa rin in the sample than the PT with a rabbit brain thromboplastin.…”

Section: Discussionmentioning

confidence: 99%

“…Results of PT and Thrombotest can be compared using the INR system. Recently, a new PT reagent based on re combinant human tissue factor and synthetic phospholipids, Innovin®, was introduced [4], The aim of the present study was to com pare the Thrombotest method, which is cur rently used in our hospital for oral anticoagu lant control, with a PT using the Innovin reagent. The influence of prolonged storage at room temperature of the blood or plasma samples on the test results was also investi gated.…”

mentioning

confidence: 99%

Comparison of a Recombinant Thromboplastin with Thrombotest® for Oral Anticoagulant Control

Baele¹,

Fiers²,

Leroux‐Roels³

1996

Thrombotest® results expressed in international normalized ratio (INR) values, obtained in 108 patients on oral anticoagulant treatment, were compared with prothrombin time (PT) results with a recombinant thromboplastin. The former results were obtained on an Amelung coagulometer, the latter on a photo-optical instrument. Using the Thrombotest method, performed within 2 h after sampling as the reference method, a first group of 63 patients had an INR value between 2 and 4. This group was considered as adequately anticoagulated and served as a true positive population in further analysis. The remaining 45 patients (true-negative group) had an INR value below 2 or higher than 4 and could thus be considered as inadequately anticoagulated. Using these definitions, a sensitivity of 86% and a specificity of 96% could be calculated for the PT with the recombinant thromboplastin. All tests from patients on oral anticoagulant treatment were also performed after 24 h storage of the blood or plasma samples at room temperature. When we compared the reference Thrombotest results with those of the late Thrombotest and the late PT recombinant thromboplastin, sensitivities of 86 and 86% as well as specificities of 91 and 96% were found, respectively. In conclusion, PT with a recombinant thromboplastin on a photo-optical instrument, even after prolonged storage of the plasma samples at room temperature, can be considered as suitable for oral anticoagulation control.