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Older Age is Risk for an International Normalized Ratio (INR) of 5 or More by G. Ribak, M. Barak, P. Froom

The elderly have higher INR values, but this may be due to factors such as inter-current illnesses or drug changes. In the following case-controlled study we contacted 304 patients receiving warfarin treatment, one group with an INR of 5 or more, and three control groups (INR < 2, 2-3.9, 4-4.9). Variables that significantly predicted an INR of 5 or more in a logistic regression model included age, the use of antibiotics, stopping of a chronic drug, and the lack of knowledge of the target INR. After forcing in other variables associated with age (less valve disease, more use of multivitamins, and a lower dose of warfarin) the increased risk was 1.6 (1.12-2.28) per 10 years of age. We conclude that age is an independent risk factor for INR values of 5 or more.

DOI: Clin. Lab. 2007;53:571-574