Laboratory tests in patients with acute appendicitis

Background: Laboratory measurements such as leucocyte count, neutrophil percentage and C-reactive protein (CRP) concentration are commonly used as diagnostic aids in patients with suspected acute appendicitis. The present study aimed to clarify the role of these laboratory tests in diagnosing acute appendicitis. Methods: The medical records of 897 patients who underwent appendicectomy for suspected acute appendicitis during a 30-month period were retrospectively reviewed. The laboratory findings were correlated with the histopathology of the excised appendices. Data were analysed to calculate the sensitivity and specificity of the individual tests, as well as the test combinations. Results: Histologically verified appendicitis was found in 740 of the 897 patients (82.5%). The rise in leucocyte count and neutrophil percentage correlated with the degree of appendiceal inflammation. The median CRP level was much higher in the patients with ruptured appendicitis compared with that in patients with a normal appendix (96.8 vs 39.6 mg/L, P < 0.001). However, patients with uncomplicated appendicitis had a lower median CRP concentration than those with a normal appendix, although the difference was not statistically significant (24.1 vs 39.6 mg/L, P = 0.079). The sensitivity of leucocyte count, neutrophil percentage and CRP in diagnosing acute appendicitis was 85.8, 87.2 and 76.5%, respectively, whereas the specificity was 31.9, 33.1 and 26.1%, respectively. Of the 740 patients with acute appendicitis, only six had all three tests simultaneously within the reference interval. Conclusions: Abnormal laboratory findings cannot reliably deliver a diagnosis of acute appendicitis. However, acute appendicitis is very unlikely when leucocyte count, neutrophil percentage and CRP level are simultaneously normal.