BMJ  2003;327:30 (5 July), doi:10.1136/bmj.327.7405.30

Primary care

Reliability of international normalised ratios from two point of care test systems: comparison with conventional methods

¹ European Concerted Action on Anticoagulation Central Facility, School of Biological Sciences, University of Manchester, Manchester M13 9PT, ² Haemostasis and Thrombosis Research Centre, Leiden University Medical Center, Leiden, Germany, ³ A Bianchi Bonomi, Haemophilia and Thrombosis Centre, IRCCS Maggiore Hospital, University of Milan, Milan, Italy, ⁴ Department of Haematology, Manchester Royal Infirmary, Manchester, ⁵ Department for Thrombosis Research, University of Southern Denmark and Department of Clinical Biochemistry, Ribe County Hospital, Esbjerg

Objective To find out how accurately two point of care test systems—CoaguChek Mini and TAS PT-NC (RapidPointCoag)—display international normalised ratios (INRs).

Design Comparison of the INRs from the two systems with a "true" INR on a conventional manual test from the same sample of blood.

Setting 10 European Concerted Action on Anticoagulation centres.

Participants 600 patients on long term dosage of warfarin.

Main outcome measures Comparable results between the different methods.

Results The mean displayed INR differed by 21.3% between the two point of care test monitoring systems. The INR on one system was 15.2% higher, on average, than the true INR, but on the other system the INR was 7.1% lower. The percentage difference between the mean displayed INR and the true INR at individual centres varied considerably with both systems.

Conclusions Improved international sensitivity index calibration of point of care test monitors by their manufacturers is needed, and better methods of quality control of individual instruments by their users are also needed.

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INRs and point of care testing

ET Murray and M Greaves
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