The Pharmaceutical Journal
Vol 271 No 7258 p75
19 July 2003

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Anticoagulation monitors need better calibration

Point-of-care anticoagulation monitors need to be better calibrated, say researchers (BMJ 2003;327:30). Furthermore, the performance of individual monitors and operators should be subject to improved methods of quality control.

Professor Leon Poller, of the school of biological sciences, University of Manchester, and colleagues compared international normalised ratios (INRs) from two point-of-care systems (the Roche CoaguChek Mini and the TAS PT-NC Rapid-PointCoag) with INRs measured using a conventional manual test. The value obtained from the manual test was considered to be the true INR. Blood from 600 patients stabilised on long-term oral anticoagulants was tested.

The team found that the INRs from the manual tests gave better agreement with two thromboplastin standards than the INRs from the monitoring systems. The first system gave higher INRs than the manual test, while the second system gave lower INRs (the researchers did not identify which system was which).

The researchers conclude: "The results indicate that additional steps in international sensitivity index calibration and quality control are essential to ensure the reliability of displayed INR of these systems." They add that other types of test monitors may have similar limitations.

In an accompanying editorial, Ellen Murray, a research fellow at the University of Birmingham, and Professor Michael Greaves, University of Aberdeen, remain positive about the value of point-of-care monitors. They say that anticoagulant control lacks precision and that the discrepancies seen in the study, though important, are not surprising.

"There are clear quality of life benefits for patients from easier access to management of oral anticoagulant treatment. All practitioners involved in the delivery of oral anticoagulant treatment should remain conscious of the limitations in the accuracy of the current systems for determining the degree of anticoagulation within individual patients," they conclude (ibid, p5).