Measurement of waist circumference for retrospective studies - prospective validation of use of CT images to assess abdominal circumference.

Introduction: To validate the use of supine position and CT images for assessing abdominal circumference (AC).

Method: A prospective study in consecutive patients undergoing scheduled abdominal CT at our center between 17 and 25 September 2012. AC was measured four times: Measurements 1 and 2 were sequentially done by the same trained nurse before abdominal CT just above the iliac crest, while measurements 3 and 4 were done on the last abdominal CT slice not showing the iliac bone. Student's t tests and Q-Q and Bland-Altman plots were used for statistical analysis.

Results: A total of 102 patients were recruited. Mean age, 60 (35-78) years. Mean BMI, 25 (18-39) kg/m(2). Mean AC, 93.2 (73-135) cm. No significant differences were found between the four ACs measured (Student's t test, P=0.83). Q-Q and Bland-Altman plots showed good overlapping for the low and central values (73-110 cm) with a greater scatter for extremely high values. For the ellipse estimation, R(2) was 0.987 with a mean error of 0.4 cm and a stretch dispersion between 1.1 and -0.3 cm.

Conclusion: Supine (either measured or estimated on CT images by free hand elliptical ROI or ellipse formula) and standing measurements appear to be equivalent for abdominal circumferences <110 cm.