Anticoagulation
===============

* David Massel

*   © 2004 Canadian Medical Association or its licensors

Jo-Anne Wilson and associates1 claim that anticoagulation clinics provided better oral anticoagulation than family physicians, but these conclusions do not appear to be supported by their study results.

First, and notwithstanding the apparent statistical significance, the difference in the proportion of time that patients' international normalized ratio (INR) values were within the desired range was less (an absolute difference of only 6%, representing a relative difference of 8%) than the authors' predefined minimally clinically important difference (10% absolute, 20% relative). Moreover, with regard to this primary endpoint, patients under the care of family physicians fared far better (76%) than the authors expected they would in the care of specialty clinics (60%).

Second, there is clearly something amiss with the percentages of patients with high-risk INRs (mentioned in the abstract, the Results and Table 2): the difference between 30% and 40% for the sample sizes in this study would not be associated with a *p* value of 0.005. Indeed, this difference is not significant at all.

Third, selective emphasis on a subgroup that has been defined post hoc (new patients with target INR of 2.0 to 3.0; see Table 3) seems inappropriate. Are the authors implying that anticoagulation clinics are not as effective if the target INR is slightly higher or if the patient has previously received anticoagulants?

Finally, the authors give the impression that all of the measures of patient satisfaction favouring anticoagulation clinics were associated with a *p* value of 0.001. Again, this is simply not possible: some of the differences reported are not significant, and those that are significant are generally far more modest.

Overall, it appears that the anticoagulation therapy provided by family physicians in this study was clinically similar to that provided in the more expensive specialty clinics.

**David Massel** University of Western Ontario London Health Sciences Centre London, Ont.

## Footnotes

*   *Competing interests:* None declared.

## Reference

1.  1. Wilson SJA, Wells PS, Kovacs MJ, Lewis GM, Martin J, Burton E, et al. Comparing the quality of oral anticoagulant management by anticoagulation clinics and by family physicians: a randomized controlled trial. CMAJ 2003;169(4): 293-8.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo5OiIxNjkvNC8yOTMiO3M6NDoiYXRvbSI7czoyMjoiL2NtYWovMTcwLzQvNDQ3LjEuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9)