Accuracy of ultrasound in a screening programme for abdominal aortic aneurysms.

OBJECTIVES: To assess the accuracy of ultrasound in the measurement of aortic diameter.

SETTING: A general practice based screening programme for abdominal aortic aneurysm.

DESIGN: (a) comparison of ultrasound with computed tomography (CT) measurement; (b) two period crossover study to assess interobserver error; (c) comparison of ultrasound measurements by technicians and radiologists.

RESULTS: In 36 patients where CT showed clear maxima in anteroposterior diameter, the measurement by ultrasound was consistently less than by CT scan (mean ultrasound-CT difference -4.4 mm, range -12.3 to 2.4 mm). There was no difference in the measurements made by different ultrasonographers, but their method of measurement produced a reading for aortic diameter less than that obtained by a vascular radiologist.

CONCLUSIONS: These results show that ultrasound measurement is less accurate for smaller aneurysms, consistently gives a smaller reading for aortic diameter when compared with CT measurement, but was reproducible between ultrasonographers. Monitoring and audit of aneurysm screening programmes to assess accuracy and reproducibility of ultrasound measurement is recommended.