Laboratory aid in the diagnosis of acute appendicitis. A blinded, prospective trial concerning diagnostic value of leukocyte count, neutrophil differential count, and C-reactive protein.

The diagnostic value of C-reactive protein (CRP), total white blood cell (WBC) count, total neutrophil count, and neutrophil differential count were evaluated in a prospective blinded study of 204 patients submitted with the tentative diagnosis of acute appendicitis. The laboratory tests were performed on blood samples obtained at the time of admission, and the results were stored until the patients were discharged. One hundred patients were operated on: 59 had appendicitis, 3 had other surgically correctable diseases, and 38 had a superfluous exploration. All 104 nonoperated patients recovered spontaneously. The sensitivity, specificity, and predictive values of single tests and test combinations were calculated at different cutoff levels. Using standard reference intervals, WBC count demonstrated the best sensitivity (83 percent) and predictive value of a negative result (88 percent). Combining the tests by an "or" rule enhanced the sensitivity to 100 percent, employing WBC count or CRP or neutrophil percentage above the reference range (triple test), but at the expense of the predictive value of a positive test (37 percent). It was concluded that both single tests and combined tests are of limited value in predicting acute appendicitis. However, the same triple test combination proved a predictive value of a negative result at 100 percent (95 percent confidence limits 92 to 100 percent), indicating that acute appendicitis is unlikely when these tests are simultaneously negative. The triple test combination was valid in 32 percent of the patients who were free from appendicitis. In the study group, 10 of the patients (25 percent) who had a superfluous exploration had a negative triple test, and they might have avoided surgery if it had been used. Therefore, the triple test is recommended as a help in reducing the significant rate of negative laparotomies in patients suspected of having acute appendicitis.