Defining the current negative appendectomy rate: For whom is preoperative computed tomography making an impact?

Background. Historically, the negative appendectomy rate (NAR) for patients operated on for acute appendicitis (AA) has exceeded 20%. We sought to define the current NAR with, increased use of computed tomography (CT) and laparoscopy. Methods. Records of 1425 consecutive patients undergoing appendectomy for suspicion of AA during the past 7 years at a single institution were reviewed. The NAR was calculated and compared with earlier data from this institution (1995-1999). Statistical methods included the Fisher exact test and the Student t test; differences of P < .05. were considered statistically significant. Results. The overall NAR was 7.65% compared to 16.3% over the period 1995-1999 (P = .0001), without a change in the perforation rate. Concurrently, the rate of preoperative CT increased from 32 % to 95 %. CT was associated with a lesser NAR only among adult females (7.6 % vs 20.8 %, P =. 005) but not among adult males or children. No difference in NAR was noted in comparing laparoscopic and open appendectomy. Patients without AA had a greater mean duration of symptoms and lower white blood cell count at presentation than those with AA. Most patients undergoing negative appendectomy had a CT, and more than 50 % had CT interpretations that were positive for, or could not exclude AA. Conclusions. The NAR in our hospital has decreased progressively to similar to 5 %. Although preoperative CT is used in almost all patients, it is only associated with a lesser NAR among adult females. False-positive CTs may contribute to the residual NAR, and further data are needed to determine. whether subgroups of male or pediatric patients benefit from preoperative CT.