Using Body Mass Index and Bioelectric Impedance Analysis to Assess the Need for Positive Oral Contrast Agents Before Abdominopelvic CT.

OBJECTIVE. The objective of this study was to determine whether body fat percentage, measured using a portable handheld bioelectric impedance analysis (BIA) device, and body mass index (BMI, weight in kilograms divided by the square of height in meters) can estimate the amount of intraabdominal and intrapelvic fat and thereby predict the need for oral contrast material before abdominopelvic CT. SUBJECTS AND METHODS. A prospective, institutional review board-approved study consisting of 101 patients who presented to the emergency department of a level I trauma center was conducted between June 1, 2016, and July 19, 2016. A medical student calculated patients' BMI and obtained body fat measurements from a handheld BIA device. Three fellowship-trained and board-certified radiologists who were blinded to the collected data then assigned a score of 1-5 on the basis of the amount of intraabdominal and intrapelvic fat seen on CT images. A McNemar test was used to compare overall sensitivity and specificity of this method, and a weighted Fleiss kappa score was used to determine interobserver variability between the three radiologists. RESULTS. Nearly all (97%) of the patients with high BMI (BMI >= 25) had sufficient amounts of intraabdominal and intrapelvic fat to allow delineation of anatomic structures without the use of oral contrast material. Of the patients with low BMI (BMI <= 21), 83% had inadequate amounts of fat to separate intraabdominal and intrapelvic structures. For patients with intermediate BMIs (21 < BMI < 25), BIA-determined body fat percentage of 30% or more can be used to predict whether a patient will have sufficient intraabdominal and intrapelvic fat to obviate oral contrast material for CT. CONCLUSION. Using BIA in addition to BMI accurately predicts amount of intraabdominal and intrapelvic fat. This information may help guide the decision to use oral contrast material in patients presenting for abdominopelvic CT.