Sensitivity and Specificity of the Neutrophil-lymphocyte Ratio in the Diagnosis of Acute Appendicitis

Acute appendicitis is a common surgical emergency; however, its misdiagnosis resulting in negative appendicectomy is not uncommon. Novel diagnostic methods will help reduce the rate of negative appendicectomy. We hypothesise that the neutrophil-lymphocyte ratio (NLR) will increase upon peritoneal involvement by inflammation, as it does in severe disease. We conducted a retrospective analysis on prospectively collected data for all emergency appendicectomy patients during the study period. We studied blood results at the time of presentation, and histology of the removed appendices. Receiver Operating Characteristics were calculated to classify histologically normal versus inflamed appendices and moderate versus severe disease. Moderate disease was that confined to the sub-serosal layers, while severe disease involved the serosa and beyond. A total of 372 patients underwent emergency appendicectomy, 254 (78.4%) of which subsequently had acute appendicitis on histology. Sixty-five (25.6%) and 189 (74.4%) patients had moderate and severe disease, respectively. The median age was 27 years (range 16-84). In diagnosing acute appendicitis, the cut-off value of the NLR was 4.2, while the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 79.5%, 67.0%, 89.8%, and 47.5%, respectively. In identifying the moderate versus severe disease, the cut-off value was 9.7, while the sensitivity, specificity, PPV and NPV were 71.4%, 53.8%, 85.4% and 43.7%, respectively. Inflammatory markers are useful adjuncts to history, examination, and radiological investigations in making the diagnosis of appendicitis. However, due to low sensitivity and specificity, they cannot be used alone. Calculation of the NLR has no additional benefit over the neutrophil count in diagnosis, or in distinguishing moderate and severe disease.