Diameter of the infrarenal aorta as a risk factor for abdominal aortic aneurysm: the Tromsø Study, 1994-2001.

Objective: We aim to study whether the diameter of the non-aneurysmatic infrarenal aorta influences the risk for abdominal aortic aneurysm (AAA) and whether the larger diameter in men can explain the male predominance in AAA.

Methods: This is a population-based follow-up study. Methods: In 4265 men and women with a normal-sized aorta in 1994-1995, 116 incident cases of AAA were diagnosed 7 years later. The risk of an incident AAA was analysed in a multiple logistic regression model according to baseline maximal infrarenal aortic diameter, adjusted for known risk factors.

Results: Compared with subjects with aortic diameter in the 21-23 mm bracket, men and women with a diameter <18mm and > or =27mm had an adjusted odds ratio (OR) of 0.30 (95% confidence interval (CI): 0.10-0.88) and 4.22 (95% CI: 1.94-9.19), respectively, for an incident AAA. When adjusted for age and baseline aortic diameter, male sex was not statistically significantly associated with the incidence of AAA (OR=1.45, 95% CI: 0.93-2.30, P=0.10).

Conclusions: Increased baseline diameter of the infrarenal aorta was a highly significant, strong and independent risk factor for developing an AAA. The larger aortic diameter in men than in women may be the most important explanation for the higher AAA risk in men.