There are several possible reasons why the VA results
differed from the other studies. The trial had substantially
longer follow-up than any of the other studies, and it may
be that over time, persons assigned to PST stop testing as
frequently, leading to a lessening of the difference between
patients who are seen every month in the anticoagulation
clinic and patients who self-test at home. Lower quality of
the VA PST intervention, which could have obscured differences
in efficacy, is possible but unlikely, given that the
PST intervention included a rigorous patient-education
program and ongoing quality control, which resulted in a
high percentage of time in the therapeutic range. Conversely,
higher quality of the control intervention (management
through the VA anticoagulation clinic) could also
obscure differences in efficacy and is more likely because
the VA trial used rigorous criteria to ensure that care in theanticoagulation clinics was state of the art (24).