shows the flow of participants through the study. The 41 000 men randomised to the two groups were balanced for age (mean (SD) 72.6 (4.7) v
72.6 (4.7) years). Screening was completed over a period of 32 months, and the median follow up was 43 (range 27-61) months. Because of the method of recording age in the electoral roll, some men were older than the target age range by the time they were invited for screening and, as a result, 725 (5.9%) of those who attended were aged 80-83 years.17
Summary of trial of screening for abdominal aortic aneurysm
Participation in screening and prevalence of abdominal aortic aneurysm
There was no difference between the numbers of men in the two groups who had had surgery for abdominal aortic aneurysm before scheduled screening (, P = 0.47, χ2test). Within the men invited for screening, the prevalence of previous surgery for abdominal aortic aneurysm was highest among those who did not attend (2.7%). Similar numbers of men in the two groups died between randomisation and scheduled screening, including 25 deaths from rupture (13 in invited group, 12 in control group). After correcting the lists for deaths, we sent letters of invitation to 19 352 men. Of these, 12 213 underwent a screening examination, a crude response fraction of 63.1%. If we excluded 1836 men who would generally be considered ineligible this figure increased to 70% ().
Elective and emergency procedures for abdominal aortic aneurysm before scheduled screening
The overall crude prevalence of any aortic aneurysms (aorta ≥ 30 mm) was 7.2%, increasing from 4.8% in men aged 65-69 years to 10.8% in the oldest men. Of the 875 cases detected, 699 (80%) aortas were 30-44 mm in diameter, 115 (13%) were 45-54 mm in diameter, and 61 (7%) were ≥ 55 mm in diameter.17
Procedures and deaths after scheduled screening
shows the numbers of procedures for and deaths from abdominal aortic aneurysm after scheduled screening. shows the corresponding numbers of events that occurred between randomisation and the end of follow up. The overall mortality within 30 days was 4.3% (7/161) after elective surgery and 24% (4/17) after surgery for ruptured aneurysms (), with no difference between study groups (P = 0.59, χ2 test). Twice as many men in the intervention group underwent elective surgery for abdominal aortic aneurysm compared with the number in the control group (107 v 54, P = 0.002, χ2 test).
Elective and emergency procedures and crude and age standardised mortality from abdominal aortic aneurysm between scheduled screening and the end of follow up
Elective and emergency procedures, deaths, and crude and age standardised mortality from abdominal aortic aneurysm between randomisation and the end of follow up
Between scheduled screening and the end of follow up 18 men died from abdominal aortic aneurysm in the intervention group and 25 in the control group (), yielding a mortality rate ratio of 0.61 (95% confidence interval 0.33 to 1.11). The age standardised mortality for those who actually attended screening was 60% lower than in the control group (7.48 v 18.91 deaths per 100 000 man years, ). Between randomisation and the end of follow up there were 31 deaths from abdominal aortic aneurysm in the intervention group and 37 in the control group, yielding a mortality rate ratio of 0.85 (0.53 to 1.36, ). Figures and show the cumulative mortality from abdominal aortic aneurysm. Men in the intervention group initially had a higher mortality, but after one year the mortality curves crossed, such that the difference between them was not significant.
Cumulative mortality due to abdominal aortic aneurysm after date of screening
Cumulative mortality due to abdominal aortic aneurysm after date of randomisation
summarises the mortality from abdominal aortic aneurysm in men aged 65-74 years and ≥ 75 years. There were no deaths among men aged 65-74 years who underwent screening and only two deaths (after scheduled screening) among those who were invited but did not attend compared with 10 in the control group, an odds ratio of 0.19 (0.04 to 0.89, P = 0.01). When we included deaths between randomisation and scheduled screening, however, we found no benefit in the younger age group (odds ratio 0.82, 0.37 to 1.84, P = 0.6).
Cumulative mortality from abdominal aortic aneurysm in men aged 64-75 years and ≥75 years
and figures and show the cumulative and age standardised all cause mortality. There is clear evidence of response bias among men who took up the invitation to be screened; their mortality experience was close to half that of invited men who did not undergo a scan. Overall, however, there were no meaningful differences in the age standardised mortality rates for all causes for the invited and control groups.
Cumulative and age standardised all cause mortality over five years after real or virtual date of screening
Cumulative all cause mortality after date of screening
Cumulative all cause mortality from date of randomisation