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Purpose For the diagnosis of acute appendicitis, the combination of clinical and laboratory variables achieves high diagnostic accuracy. Nevertheless, appendicitis can present with normal laboratory tests of inflammation. The aim of this study was to investigate the incidence of normal inflammatory markers in patients operated for acute appendicitis. Methods This is an analysis of data from a prospective, multicentre SNAPSHOT cohort study of patients with suspected acute appendicitis. Only patients with histopathologically proven acute appendicitis were included. Adult patients with acute appendicitis and normal preoperative inflammatory markers were explored further in terms of abdominal complaints, preoperative imaging results and intraoperative assessment of the degree of inflammation and compared to those with elevated inflammatory markers. Results Between June and July 2014, 1303 adult patients with histopathologically proven acute appendicitis were included. In only 23 of 1303 patients (1.8%) with proven appendicitis, both preoperative white blood cell count and C-reactive protein levels were normal. Migration of pain was reported less frequently in patients with normal inflammatory markers compared to those with elevated inflammatory marker levels (17.4% versus 43.0%, p = 0.01). Characteristics like fever, duration of symptoms and localized peritonitis were comparable. Only 4 patients with normal inflammatory markers (0.3% overall) had complicated appendicitis at histopathological evaluation. Conclusion Combined normal WBC and CRP levels are seen in about 2 per 100 patients with confirmed acute appendicitis and can, although rarely, be found in patients with complicated appendicitis.

Introduction In patients treated with an appendectomy for acute appendicitis, the specimen is generally sent for histological evaluation. In an era of increasing non-operative treatment for acute appendicitis, it is important to know the incidence, the diagnostic accuracy, and treatment consequences of appendicular neoplasms that are found in acute appendicitis. We hypothesize that pre- and intra-operative parameters might predict an appendicular neoplasm. Methods Data was used from our previous prospective observational cohort study. All patients undergoing surgery for suspected acute appendicitis were included. The primary outcome was the incidence of appendicular neoplasms in patients operated for acute appendicitis. Secondary outcomes were pre-operative diagnostics and imaging outcomes, intra-operative surgical judgment, and postoperative management and outcome. Possible predictors of an appendicular neoplasm were identified and used in multivariable logistic regression. Patients with an appendicular neoplasm were followed for 3 years after initial appendectomy. Results A total of 1975 patients underwent surgery for suspected acute appendicitis and in 98.3% (1941/1975) the appendix was removed. In 1.5% (30/1941) of these patients, an appendicular neoplasm was found. Among the malignant neoplasms, the majority were grade 1 neuroendocrine tumors (NET) in 65% (13/20). On pre-operative imaging, there was no suspicion of malignancy. In three cases, there was an intra-operative suspicion of malignancy. Multivariable analysis showed only age as an independent predictor for appendicular neoplasms. No recurrent or new malignancy was found during follow-up. Discussion The incidence of appendicular neoplasm in patients undergoing an acute appendectomy is very low and clinical risk factors could not be identified.