Background and Objectives: Acute abdominal pain in children has been noticed to be a primary reason to seek medical attention in multisystem inflammatory disorder (MIS-C), which can prevail separately or together with acute appendicitis. Our aim was to distinguish regular appendicitis cases from MIS-C and to suggest the best clinical and laboratory criteria for it. Materials and methods: Cases of patients, admitted to the Pediatric Surgery Department over a six-month period in 2021, were retrospectively analyzed. Confirmed MIS-C or acute appendicitis cases were selected. MIS-C cases were either separate/with no found inflammation in the appendix or together with acute appendicitis. Acute appendicitis cases were either regular cases or with a positive COVID-19 test. Four groups were formed and compared: A-acute appendicitis, B-MIS-C with acute appendicitis, C-MIS-C only and D-acute appendicitis with COVID-19. Results: A total of 76 cases were overall analyzed: A-36, B-6, C-29 and D-5. The most significant differences were found in duration of disease A—1.4 days, B—4.5 days, C—4 days, D—4 days (p < 0.0001), C reactive protein (CRP) values A-19.3 mg/L B-112.5 m/L, C-143.8 mg/L and D-141 mg/L (p < 0.0001), presence of febrile fever A-13.9%, B-66.7%, C-96.6% and D-40% (p < 0.0001) and other system involvement: A 0%, B 100%, C 100% and D 20%. A combination of these factors was entered into a ROC curve and was found to have a possibility to predict MIS-C in our analyzed cases (with or without acute appendicitis) with an AUC = 0.983, p < 0.0001, sensitivity of 94.3% and specificity of 92.7% when at least three criteria were met. Conclusions: MIS-C could be suspected even when clinical data and performed tests suggest acute appendicitis especially when at least three out of four signs are present: CRP > 55.8 mg, symptoms last 3 days or longer, febrile fever is present, and any kind of other system involvement is noticed, especially with a known prior recent COVID-19 contact, infection or a positive COVID-19 antibody IgG test.

Background and Objectives: Our aim was to see if the COVID-19 pandemic led to an increase of time until diagnosis, operation, and time spent in Emergency room (ER), and if it resulted in more cases of complicated appendicitis and complication rates in children. Materials and Methods: We conducted a retrospective analysis of patients admitted to the Pediatric Surgery Department with acute appendicitis during a 4-month period of the first COVID-19 pandemic and compared it to the previous year data—the same 4-month period in 2019. Results: During the pandemic, the time spent in the ER until arriving at the department increased significantly 2.85 vs. 0.98 h p < 0.001, and the time spent in the department until the operation 5.31 vs. 2.66 h, p = 0.03. However, the time from the beginning of symptoms till ER, operation time and the length of stay at the hospital, as well as the overall time until operation did not differ and did not result in an increase of complicated appendicitis cases or postoperative complications. Conclusions: The COVID-19-implemented quarantine led to an increase of the time from the emergency room to the operating room by 4 h. This delay did not result in a higher rate of complicated appendicitis and complication rates, allowing for surgery to be postponed to daytime hours if needed.