A statistical analysis of the growth of small abdominal aortic aneurysms.

Screening for abdominal aortic aneurysm has been offered to 13,000 patients. An overall compliance of 76% (range 51-99%) has been achieved. For those with an initial aortic diameter between 29 mm and 45 mm serial ultrasound scans are offered to monitor aortic change. Of the 302 cases followed up by repeated scans, 93 have had more than 5 scans (mean of 7 scans) over a mean time period of 32.1 months (range 15-63 months). The rate of change of all these aneurysms has been calculated using all data points and robust linear regression. It has been possible to postulate an algorithm for aortic growth. The influence of measurement precision and ultrasound quality assurance on the rescan interval is demonstrated and it is suggested that 2 years is a suitable rescan interval for aortas with diameter less than 40 mm.