Influence of three types of automated coagulometers on the international sensitivity index (ISI) of rabbit, human, and recombinant human tissue factor preparations--a multicenter study.

Five tissue factor reagents and three types of automated instruments for prothrombin time (PT) determination were studied in an international multicenter collaborative exercise. The purpose of this work was to determine the international sensitivity index (ISI) for each combination of reagent and instrument against the international reference preparation RBT/90. Each type of instrument was used by 3 or 4 centers to assess the interlaboratory variation of the ISI.

Control of oral anticoagulation in patients with the antiphospholipid syndrome--influence of the lupus anticoagulant on International Normalized Ratio. Groupe Méthodologie en Hémostase du Groupe d'Etudes sur l'Hémostases et la Thrombose.

The recommended therapeutic range of International Normalized Ratio (INR) for oral anticoagulant treatment in patients with the antiphospholipid syndrome remains controversial. As a part of this controversy, it has been suggested that lupus anticoagulants (LA) could interfere with the determination of prothrombin time, thus questioning the validity of monitoring the treatment of these patients using INR. To clarify this point, we compared the values of INR obtained in the plasmas of two groups of patients, one without LA (n = 47), and the other with LA (n = 43).

Multicenter study of an erythro-aggregometer: quality control and standardization.

There is a need for quality assurance procedures in hemorheology, especially for clinical and pharmacological studies, which require reliable and well-calibrated instruments to be interpretable and comparable. Preliminary investigations allowed preparation of standardized SM (normal NS and hyperaggregable HS), and checking of storage conditions (in accordance with the guidelines of the SSC of ISTH) of RBC in nutritive SAG mannitol for at least 2 or 3 weeks with subsequent washings and resuspension in SM. In our study, we compared erythro-aggregometers of the same brand in 6 laboratories, using the same red blood cells (RBC) and suspending media (SM) for each series of tests.

Long-term French experience in INR standardization by a procedure using plasma calibrants.

The International Normalized Ratio (INR) has not lowered the interlaboratory differences in prothrombin time (PT) values to the extent expected, mainly because of the instrument-dependency of the International Sensitivity Index (ISI) and other factors (eg, accurate determination of the ISI, the normal value used in the PT ratio). The procedure (PPC) using plasma calibrants (reference lyophilized plasmas with assigned activity) has been evaluated since 1977 in nine French national external quality assessment surveys (NEQAS) involving approximately 4,000 laboratories and numerous local thromboplastin technique combinations. The PPC was compared with the conventional procedure (using the manufacturer's ISI), and the efficiency of antivitamin K-calibrated (AK Cal) plasmas from patients receiving oral anticoagulants vs artificially depleted plasma calibrants was also evaluated.

Validation protocol of analytical hemostasis systems: measurement of anti-Xa activity of low-molecular-weight heparins.

A standard validation protocol adapted to the chromogenic assay of anti-Xa activity of low-molecular-weight heparins was used in a multicenter study to assess its suitability for comparing and evaluating analytical hemostasis systems. The protocol included: familiarization with the system (repeatability); assessment of limits of linearity, detection limits, and cross-contamination; and validation (reproducibility and accuracy of measurements of treated patients' plasmas). We calibrated the systems with the same range of lyophilized plasmas daily and evaluated repeatability and reproducibility by using a single batch of lyophilized plasmas at three anti-Xa activities.