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Self-testing INR no better than clinic tests

By Nigel Praities

Self-testing INR levels provides few major benefits over clinic testing in patients taking warfarin, say US researchers.

The researchers randomly assigned 3,000 patients taking warfarin due to mechanical heart valves or atrial fibrillation either to weekly self-testing of INR or monthly testing in a clinic and followed them for two to five years.

Those in the self-testing group did not have a significantly longer time to their first major event – stroke, a major bleeding episode or death – compared with those in the clinic testing group.

Over the entire follow-up period, the self-testing group had a small but significant improvement in the percentage of time during which their INR was in the required range, but also had an increased rate of bleeding, compared with those in the clinic testing group.

Study lead Dr David Matchar, director of the centre for clinical health policy research at Duke University School of Medicine, North Carolina, said: ‘The results do not establish the superiority of self-testing over high quality clinic testing in preventing major clinical outcomes, but do provide evidence of modest improvements over time in the therapeutic INR range, patient satisfaction with anticoagulation therapy, and quality of life.’

NEJM 2010; 363: 1608-20