Accuracy of international normalized ratio determined by portable venous-blood coagulation monitor versus a central laboratory.

BACKGROUND

The CoaguChek is a portable monitor unit for measuring the international normalized ratio (INR). The purpose of the study was to evaluate the accuracy of a portable prothrombin time (PT) monitor (CoaguChek, Roche Diagnostics, Mannheim, Germany) compared with the laboratory method.

MATERIAL AND METHOD

Paired venous blood INRs were performed in 220 consecutive outpatient tests mainly in anticoagulated (n = 210) and non-anticoagulated (n = 10) individuals. Accuracy was evaluated in 220 tests by parallel assessment of INRs (CoaquChek and laboratory). Accuracy was determined using statistic regression analysis and clinical agreement (expanded and narrow criteria). Agreement in dual INR measurement also was evaluated as a function of increasing INR.

RESULTS

The CoaguChek significantly correlated with the laboratory measurement (r = 0.89). The proportion of dual INR measurements that satisfied the clinical relevant expanded, and narrow agreement criteria was 90 per cent and 86 per cent respectively. Eighty-two per cent of all dual measurements were within 0.5 INR units. The accuracy of the portable monitor was greatest for INR values less than 3.0; above this INR level the portable monitor overestimated laboratory INR values.

CONCLUSIONS

The CoaguChek is an accurate alternative to laboratory assessment of INR at values < 3.0. The authors suggest the use of the monitor in non anticoagulated patients or anticoagulated patients at values less than 3, as most physicians in Thailand prefer lower INR than in Western countries.