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Thromb Haemost 1989; 61(02): 166-169
DOI: 10.1055/s-0038-1646552
Original Article
Schattauer GmbH Stuttgart

A Multi-Centre Study to Evaluate Method Dependency of the International Sensitivity Index of Bovine Thromboplastin

R H M Peters
1   The Laboratory for Clinical Chemistry and Haematology, Hospital “De Stadsmaten”, Enschede, The Netherlands
,
A M H P van den Besselaar
2   The Thrombosis and Haemostasis Research Unit, Department of Haematology, University Hospital Leiden, The Netherlands
,
F M F G Olthuis
1   The Laboratory for Clinical Chemistry and Haematology, Hospital “De Stadsmaten”, Enschede, The Netherlands
› Author Affiliations
Further Information

Publication History

Received 20 September 1988

Accepted after revision 17 November 1988

Publication Date:
30 June 2018 (online)

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Summary

In The Netherlands, a particular coagulometer method for prothrombin time (PT) determination with reduced sample and reagent volumes is used by 62% of the laboratories controlling oral anticoagulant therapy. This “micro-method” has been calibrated against the manual tilt-tube technique for PT determination by six Dutch laboratories. Each laboratory tested 20 fresh normal blood samples and 60 fresh patient blood samples using both methods with the same batch of bovine thromboplastin reagent, according to a detailed protocol. Both methods were comparable as to their precision, but PTs measured by the micromethod were significantly prolonged (p <0.001, Student’s t-test) as compared to the manual method. This effect is stronger for samples of normal subjects than for patients’ samples. It was assumed that the International Sensitivity Index (ISI) of the bovine thromboplastin for the manual method was 1.00 in each laboratory. The ISI-values of the bovine thromboplastin for the micro-method determined by the six laboratories ranged from 1.00 to 1.07 (mean 1.03, SD 0.03). Our results indicate that any other laboratory, using this thromboplastin and the micromethod, should obtain accurate assessment of the International Normalized Ratio from their own mean normal PT and an ISI which is 3% higher than the ISI supplied by the thromboplastin manufacturer for the manual tilt-tube method.

Keywords

International Sensitivity Index - International Normalized Ratio - Oral anticoagulant control - Prothrombin time
 

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