Warfarin treatment complications do not correlate to cTTR when above 70

The mean time in target range for each centre, cTTR, has previously been shown to correlate to the rate of complications in poorly managed warfarin treatment. However less is known about the correlation when warfarin treatment is well managed.

The aim of this study was to examine the correlation between cTTR and the rate of complications in a real life setting with cTTR above 70%, with focus on patients with warfarin due to atrial fibrillation or secondary prevention of a VTE.

In total 66,605 patients with 89,293 treatment periods, corresponding to 179,624 treatment years, with warfarin treatment due to VTE or AF between January 1st 2006 and December 31th 2011, was retrieved from the national quality register AuriculA. The cohort was matched with the National Patient Register in Sweden for complications and background characteristics.

We found 172 centres and 68,797 treatment periods for AF and 166 centres and 20,496 treatment periods for VTE. Over 90% of the patients had a target range between INR 2-3. We found no correlation between increasing cTTR and reduction in the rate of complications for the AF patients. However, for VTE patients we saw a correlation between increasing cTTR and a reduced complication rate.

Our results show that at very high cTTR levels, above 70%, further improvements in cTTR do not correlate to less treatment complications at least for patients with AF.