Dietary interactions and INR variability: retrospective evaluation of patients couples on oral anticoagulant therapy

Aim. The association between dietary vitamin K intake and International Normalized Ratio (INR) variability in patients on oral anticoagulants treatment (OAT) has been evaluated in several studies. Changes in diet composition are known to lead to INR variability. We evaluated INR over time in married couples on OAT and non-cohabitant couples on OAT, to assess clinical relevance of the diet. Methods. Among outpatients receiving OAT we selected 31 married couples. Husbands and wives were then matched by demographic and clinical characteristics to 31 men and 31 women on OAT not married nor living together. We analyzed 6,357 INR measurements recorded from February 1998 to November 2009. Results. We found similar average INR values within married couples and also within non-cohabitant couples. Using mixed models we confirmed INR differences between seasons and the slightly lower INR in non-cohabitant couples compared to married couples; although statistically significant, they were of marginal clinical significance. Conclusion. Within both married and non-cohabitant couples, we did not find statistically or clinically significant differences between men and women over time. The lack of INR differences over time within non-cohabitant couples indicates that diet is not an important determinant of INR over time. Also seasonal INR variations and differences between married and non-cohabitant couples were of little practical importance.