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

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.