Unnecessary appendectomy can cause complications; ways of reducing negative appendectomy rates (NAR) using biochemical and imaging methods are desirable. We retrospectively examined 640 patients who underwent appendectomy for suspected AA. Patients with histologically confirmed appendicitis were designated the positive appendectomy group (n = 565), whereas those with unconfirmed appendicitis were designated the negative appendectomy group (n = 75). The positive appendectomy group was subdivided into the non-perforated (n = 511) and perforated (n = 54) appendectomy groups according to pathology reports. We compared the age, sex, lymphocyte count, neutrophil percentage, pathologic positivity or negativity for appendicitis, C-reactive protein (CRP) level, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) of the patients. When the perforated, non-perforated, and negative appendectomy groups were compared, the highest CRP level, NLR, and PLR were evident in the perforated appendectomy group (p = 0.001), whereas the lowest neutrophil percentage was found in the non-perforated appendectomy group (p = 0.001). Multiple logistic regression analysis identified neutrophil percentage, CRP value, and NLR as independent variables and demonstrated that AA could be diagnosed with 88.9 % accuracy using the cutoff values determined. In patients with suspected AA, particularly in rural areas with limited access to advanced imaging modalities, the evaluation of neutrophil percentage, CRP level, and NLR, in combination with the findings of a physical examination, may aid diagnosis and reduce NAR.