Appendicitis, body mass index, and CT: is CT more valuable for obese patients than thin patients?

The purpose of our study is to determine whether body mass index (BMI = weight in kg/height in meters(2)) was related to the rate of negative appendectomy in patients who underwent preoperative CT. A surgical database search performed using the procedure code for appendectomy identified 925 patients at least 18 years of age who underwent urgent appendectomy between January 1998 and September 2007. BMI was computed for the 703 of these 925 patients for whom height and weight information was available. Patients were stratified based on body mass index (BMI 15-18.49 = underweight; 18.5-24.9 = normal weight; 25-29.9 = overweight; 30-39.9 = obese; ≥ 40 = morbidly obese). Negative appendectomy rates were computed. Negative appendectomy rates for patients who did and did not undergo preoperative CT were 27 per cent and 50 per cent for underweight patients, 10 per cent and 15 per cent for normal weight patients, 12 per cent and 17 per cent for overweight patients, 7 per cent and 30 per cent for obese patients, and 10 per cent and 100 per cent for morbidly obese patients. The difference in negative appendectomy rates for overweight patients, obese patients, and morbidly obese patients who underwent preoperative CT as compared with patients in the same BMI category who did not undergo preoperative CT was statistically significant (P ≤ 0.001). The negative appendectomy rates for overweight patients, obese patients, and morbidly obese patients who underwent preoperative CT were significantly lower than for patients in these same BMI categories who did not undergo preoperative CT.