Summary
The 512 Coagulation Monitor is a portable coagulation photometer that uses disposable
cartridges containing a lyophilized rabbit brain thromboplastin to measure the PT
for capillary whole blood. It has been proposed as a suitable system for patient self
monitoring at home, but its performance has never been thoroughly assessed for results
expressed as International Normalized Ratio (INR). In particular, there is no available
information about the adequacy of the WHO calibration model with the Monitor. The
aims of the study were to determine the International Sensitivity Index (ISI) against
the secondary International Reference Preparation for rabbit thromboplastin and to
assess the precision of the INR. The study demonstrates that the Monitor can be calibrated
with the WHO model, because log-transformed PTs for patients stabilized on oral anticoagulants
and normal individuals are linearly related and because the same orthogonal regression
line describes patient and normal data points adequately. However, the ISI calculated
in this study (2.715) is higher than that adopted by the manufacturer (2.036). The
between-assay reproducibility of the Monitor is acceptable (CV = 9.7%) with results
expressed in seconds, but become unacceptably poor when the results are converted
into INR (CV = 18.8%) because of the high ISI value of the thromboplastin used. We
think that the Monitor might be suitable for monitoring oral anticoagulant therapy
if the manufacturer would provide a more sensitive thromboplastin in the cartridges.
