Straight to CT: Using Body Mass Index (BMI) to Guide First-Line Imaging Selection in Suspected Cases of Acute Appendicitis

Purpose: Appendicitis, the most common surgical emergency, heavily relies on imaging for proper diagnosis. Due to its availability and relatively low cost, current clinical guidelines recommend point-of-care or formal ultrasonography (US) as first-line imaging, which provides varying degrees of diagnostic accuracy. The current study explores the relationship between BMI and the diagnostic effectiveness of US in suspected cases of acute appendicitis.

Methods/Materials: We gathered data on adult subjects (age ≥ 18 years) with possible appendicitis and who underwent right lower quadrant US over a 1 year period via retrospective chart review of an integrated healthcare system’s electronic database. Univariate and multivariable logistic regression analyses evaluated the association between demographic and clinical characteristics of subjects and US diagnostic accuracy.

Results: 351 subjects underwent US during the study period. Subjects with a concordant US (where the diagnosis from US imaging correctly aligned with the final clinical and pathological diagnosis) had a significantly lower BMI. In multivariable logistic regression of nongravid adults, a high BMI (defined as ≥ 25) was associated with half the odds of a concordant appendicitis diagnosis via US compared to those with a BMI < 25. Gravid females were excluded from our main analysis due to perfect collinearity between pregnancy and gender. A separate univariate logistic regression of all women demonstrated significant predictive effects of BMI and pregnancy status on US diagnosis concordance; however, these effects were not maintained in multivariable logistic regression. Finally, although over a fourth of subjects received CT imaging following the initial US, the only significant predictor of receiving additional CT imaging was leukocytosis.

Conclusions: To minimize treatment delay and increase cost effectiveness, the use of CT as the first line imaging modality in suspected cases of appendicitis is recommended in nongravid patients with a BMI ≥ 25 because of the significantly decreased odds of an accurate US among overweight patients.