A systematic review of outcome measures reported for the therapeutic effectiveness of oral anticoagulation. (Original Article).

Aims: To evaluate the evidence of therapeutic international normalised ratio (INR) control reporting and to provide recommendations for future reporting, particularly for research and audit purposes.

Methods: A systematic review of literature published over a five year period describing therapeutic INR control. Papers were identified from the Medline electronic database, and those that met the quality criteria were reviewed independently by an academic general practitioner and a consultant haematologist.

Results: Fifteen papers were identified that met the quality criteria for review. The sample size of studies ranged from 53 to 2545 (mean, 483.9) patients. Follow up ranged from three months to 13 years. Twelve studies reported results from secondary care only, one from primary care only, and two from both primary and secondary care. Seven of the 15 papers reported percentage time in range, five of 15 papers reported mean INR, six of 15 papers reported the proportion of tests in range, and five of 15 papers reported mean warfarin dose. Additional methods of presenting INR results were: dose changes each month, distribution of INR results, deviation of INR value from mean, percentage dose changes, time between visits, and median INR value. Six papers reported only one outcome measure, six reported two outcomes, two papers reported three outcomes, and one paper reported five outcomes.

Conclusions: It is recommended that at least two outcome measures should be reported and measures should be selected so that both the INR determinations and dosing advice are monitored.

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The past few years have seen an increase in interest in the therapeutic management of oral anticoagulation. Principally, this has been driven by the increasing numbers of patients receiving oral anticoagulation treatment as a result of trials demonstrating the effectiveness of oral anticoagulation in preventing strokes in patients with atrial fibrillation. (1) One criticism of the original studies demonstrating the effectiveness of oral anticoagulation in preventing stroke was that although target international normalised ratios (INRs) for treatment were stated, the achieved intensity of anticoagulation achieved was not. This is an important issue because achieved intensity of anticoagulation is related to the benefit derived from the treatment. Similarly, subsequent studies have used a wide range of outcome measures to determine performance levels of both individuals and anticoagulation clinics. Our own research has shown that using different outcome measures of anticoagulant clinic effectiveness produced di fferent results on the same data sets. (2 3) The need for standardisation has previously been highlighted. (4)

"The aims of our study were to establish the nature of outcome measures being reported for the therapeutic effectiveness of oral anticoagulation and to provide recommendations for international normalised ratio reporting in the future"

To our knowledge, there have been two attempts to introduce some standardisation into the process, with the description of point prevalence (5) (or last look in the book) and the per cent time spent in range. (6) It is now widely accepted that per cent time in range should be calculated assuming a linear change in INR values over time. (7) However it is not clear how widely these outcome measures are used. We have undertaken a …