Evidence about the consequences of false positive, false negative and incidental findings of using AAA screening from a safety perspective are scarce in the literature. However, the available data indicate that the magnitude of the estimates would be low. An evaluation of the screening programme of Huntingdon (UK) found no false negatives when comparing ultrasound results with further ruptures. They also found no false positives when comparing ultrasound with computed tomography. They reported ultrasound sensitivity of 100% for detecting AAAs of 4.5 cm or more, specificity of 100% for AAAs of up to 3.0 cm, and therefore 100% for both positive and negative predictive values {19}.

Lindholt JS et al. {20} estimated accuracy from the inter-observer values. Their estimated sensitivity, specificity and predictive values of a positive test for AAA in the distal part of the infrarenal aorta were 98.9%, 99.8% and 97. 0%, respectively. The sensitivity, specificity and predictive value of a positive test for AAA in the proximal part of the infrarenal aorta were estimated at 87.4%, 99.9%, and 94.7%.

Based on the previous figures we calculated false positive and false negative rates (ratio of false positives to non-cases and ratio of false negatives to cases respectively). The false positive and false negative rates of AAA in the distal part of the infrarenal aorta using ultrasonography were 0.0013 and 0.0107 respectively {20}. The false positive and false negative rates of AAA in the proximal part of the infrarenal aorta found using ultrasonography were 0.0006 and 0.1260 respectively {20}. The incidence of false-positive scans is small and of little clinical consequence as they are likely to be detected on surveillance rescanning or confirmatory computed tomography (CT) scan. A false negative finding would result in same outcomes as those occurring in subjects for whom screening was not performed.

Ultrasound has high accuracy values when used as the first diagnostic test in AAA screening programmes; however some difficulties with visualising the aorta may occur in some cases (1.2% in the MASS trial){8}. The MASS trial, which performed the screen in non-routine clinics using portable ultrasound machines, had 1.2% non-valid ultrasound tests. Therefore, it is advisable for some cases to be re-scanned in a hospital setting by experienced sonographers.

The AAA screening clinical trials have not reported incidental discoveries of other pathologies. According to the clinical trials the frequency of incidental discovery of other pathologies in screening programmes for AAA would be low.