
Acute appendicitis is the common cause of surgery for acute abdominal pain in children. The diagnosis of acute appendicitis in pediatric patients remains a challenge internationally. This disease is most common among patients between the age of 10 and 19 years old. The aim of the study was to evaluate whether neutrophil-lymphocyte ratio (NLR) and ultrasound (US) results on admission could aid the diagnostic accuracy of the Pediatric Appendicitis Score (PAS) in pediatric patients with suspected acute appendicitis. Our study was performed on 480 children admitted for suspected acute appendicitis and underwent appendectomy at the MCHHC, Ulaanbaatar Mongolia, between May 2019 and December 2019. Patients were categorized into three groups based on the value of their PAS. The diagnosis of appendicitis was confirmed postoperatively with a histological study. Negative (NPV) and positive predictive values (PPV) of PAS, NLR and ultrasound were calculated. In the diagnosis of acute appendicitis in pediatric patients, the NLR and ultrasound methods are equivalent in terms of diagnostic accuracy. In children with a PAS value of 4 and 5, it more effective to use a combination of ultrasound and NLR to diagnose accurately.