Elsevier

Thrombosis Research

Volume 92, Issue 1, October 1998, Pages 11-17
Thrombosis Research

REGULAR ARTICLE
Accuracy of a Portable International Normalization Ratio Monitor in Outpatients Receiving Long-Term Oral Anticoagulant Therapy: Comparison with a Laboratory Reference Standard Using Clinically Relevant Criteria for Agreement

https://doi.org/10.1016/S0049-3848(98)00098-XGet rights and content

Abstract

The accuracy of a new, portable INR monitor (CoaguChek, Boehringer-Mannheim, Indianapolis, IN) was evaluated by comparing INR results from the portable monitor with results obtained by a laboratory-based method. Dual INR measurements (portable monitor, laboratory) were performed in 163 consecutive outpatients receiving warfarin. Agreement in dual INR measurements was defined based on clinically-relevant expanded and narrow criteria and statistical criteria. Agreement in dual INR measurements also was evaluated as a function of increasing INR. The proportion of dual INR measurements that satisfied the clinically-relevant expanded, and narrow agreement criteria was 90%, and 86%, respectively. Seventy-nine percent 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 underestimated laboratory INR values. The proportion of dual INR measurements within 0.5 INR units for laboratory INR ranges of <2.0, 2.0 –3.0, 3.1–4.0, and >4.0 was 98%, 87%, 57%, and 21%, respectively. We conclude that the portable INR monitor achieved a clinically acceptable level of accuracy when compared to the traditional laboratory method and provides a suitable alternative method of monitoring the INR in patients receiving warfarin.

Section snippets

Patients

Consecutive ambulatory patients who were receiving long-term warfarin, for at least 3 months, and who were followed by the Anticoagulant Clinics of St. Joseph’s Hospital in Hamilton, Ontario, and the Reseau Sante de Richelieu-Yamaska in St. Hyacinthe, Quebec between January and October 1996 were eligible for this study. All patients participating in this study provided informed consent.

Study Protocol

All patients underwent blood testing during the same clinic visit to determine the INR using two methods.

Patients

Dual INR measurements using the portable monitor and laboratory methods were determined in 163 patients who were receiving long-term warfarin. The clinical characteristics of the patients is summarized in Table 1. In 132 patients with chronic atrial fibrillation or venous thromboembolism, the targeted INR was 2.0–3.0; in 10 patients with a tilting mechanical heart valve, the targeted INR was 2.5–3.5; in 21 patients with a ball-cage mitral mechanical heart valve or a history of systemic

Discussion

In this study, we investigated the accuracy of a new, rapid-response, portable INR monitor as compared with the conventional laboratory method to measure the INR in patients receiving long-term warfarin. Unlike other studies evaluating the accuracy of portable INR monitors, we attempted to use clinically relevant criteria to evaluate agreement between portable monitor and laboratory INR measurements. Based on our analysis, we conclude that the CoaguChek monitor achieved a clinically acceptable

Acknowledgements

We are indebted to Ms. Mimi Orescanin for her valuable technical and administrative assistance. Dr. Ginsberg is a recipient of a Career Investigator Award from the Heart and Stroke Foundation of Ontario. Dr. Lane is the Director of Scientific Affairs, Boehringer-Mannheim, Canada.

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