Appendicitis poses a challenge throughout the entire process from diagnosis to effective treatment in paediatric patients. Considering that non-surgical or conservative treatment is used to treat acute appendicitis (AA) in children, this leads to one of the most important emergent problems in paediatric surgery – to differentiate between acute uncomplicated appendicitis (AuA) and acute complicated appendicitis (AcA) during the onset of treatment because AcA attests to the delayed diagnostic processes and requires only emergency surgical treatment. In Latvia, AcA occurs in more than 35 % of cases. Our previous studies have shown that at the Children's Clinical University Hospital (CCUH) Riga, Latvia, the total number of operated AA cases remains unchanged, however, the number of AcA cases is increasing. The current diagnostic dilemmas of AcA show the need to search for new early diagnostic indicators in paediatric patients in order to reduce the incidence of complications and prevent lethal risks. The first challenge in the diagnosis of AA is the differentiation between AA and differential diagnoses that are non-appendicitis (nAA). Currently, the diagnosis of AA relies on typical clinical findings, anamnesis and the Alvarado score, all of which lack sensitivity and specificity and rely on the cooperation and fluency of patients and/or their carers. Other techniques such as computed tomography (CT) and diagnostic laparoscopy are used, but the negative aspects outweigh the productivity of the diagnostic value (Podany et al., 2017). The introduction of ultrasound (US) imaging and blood test values (leucocytosis and an increased C-reactive protein (CRP)) as diagnostic tools has decreased the need for diagnostic laparoscopies, but despite this, the current negative appendectomy rate is still at 1–40 % (Maloney et al., 2019). This research primarily aims to find a more productive solution to effectively diagnose AA by differentiating between AA and nAA. It is already known that AcA is an inflammation of the complex origin of the appendix. Although it was traditionally considered to be simply an obstruction of the appendiceal lumen, there is increasing evidence that the disease can be caused by specific pathogenic microorganisms, with Yersinia enterocolitica being more specific (Fernandes et al., 2020). Some previous studies have confirmed a polymicrobial process, but it is not yet possible to identify the main pathogen and its source (Rogers et al., 2016); (Salö et al., 2017); (Bhattacharya et al., 2022); (Camacho-Cruz et al., 2022). This has also led to increased interest and research in antibiotic therapy as a non-invasive treatment for AA. The increased use of antibiotics raises questions about the prevalence of microorganisms as causative agents in appendicitis, which is the focus of the present study. Differentiation between AuA and AcA is also an increasing problem, especially in emergency situations, and the prevalence of specific microorganisms for each of these classifications essentially leads to a different antibiotic treatment strategy. Therefore, this study additionally aims to identify which microorganisms are more prevalent in AuA and AcA respectively as well as the subsequent proposed antibiotic strategy. This also leads to the challenging task of rapid confirmation of AA and further differentiation between AuA and AcA in an emergency. Atypical differentiation and multiple differential diagnoses are two of many factors that hinder this rapid confirmation. Therefore, this study aims to further enable rapid diagnosis of AA and differentiation between AuA and AcA in an emergency setting. The focus on immunological pathways is expanding and, consequently, the number of proposed biomarkers is increasing, although none has achieved widespread use to date (Selleck et al., 2017). The search for the optimal biomarker may be futile, but in combination with a medical history and clinical findings, it is possible to improve the quality of diagnostic approaches, thereby reducing complications and overall hospital costs incurred by reducing unnecessary imaging and surgery. This was a prospective cohort study. The patients were divided into three groups: AcA (acute complicated appendicitis), AuA (acute uncomplicated appendicitis) and a Ctr (control group). Out of a total of 153 patients, 97 had AA (acute appendicitis) and 56 were in the Ctr. Our results show that urine leucine-rich alpha-2 glycoprotein 1 (LRG1) is an accurate marker in confirming the diagnosis of AA. The concentration of serum and urine LRG1 is useful in detecting the severity of AA with respect to AcA and AuA. The biomarker serum neutrophil gelatinase-associated lipocalin (NGAL) increases significantly on Day 0 and should be used in the differential diagnosis of acute abdominal pain. CRP and serum interleukin-6 (IL-6) remain non-specific biomarkers due to limitations and can be used to diagnose AA and differentiate AcA from AuA. Pseudomonas aeruginosa is more commonly identified in acute complicated appendicitis and is susceptible to agents of the cephalosporin group, such as ceftazidime. However, P. aeruginosa has phenotypic resistance to cefotaxime; therefore, cefotaxime should be excluded from empirical treatment of acute complicated appendicitis. Antibiotic treatment strategies for acute complicated appendicitis should include antibiotics with different mechanisms of action to achieve a synergistic effect and prevent the development of antibiotic resistance. The incidence of extended-spectrum beta-lactamase (ESBL)-producing microorganisms was low in these cases of acute appendicitis. Serum antibodies to Yersinia enterocolitica were not detected in AA patients and therefore cannot be used to predict of AA. Research into the appendix microbiome and the new biomarkers NGAL and LRG1 in blood serum and LRG1 in urine may provide a better understanding of complicated acute appendicitis in terms of etiopathogenesis and early diagnostic accuracy, as well as timely diagnosis of disease severity and possible disease prognosis. It should be emphasised that the results of the study in Latvia could improve the quality of medical care in other countries. The obtained results can also contribute beyond the borders of Latvia, as they have been published in international databases, as well as the text of the doctoral thesis is in English, so that other colleagues who are interested in this topic can familiarise themselves with the researched material and it is possible to introduce changes in their daily practice in connection with in paediatric patients with acute appendicitis. 3.2 Clinical Medicine; Sub-Sector – Surgery (Paediatric Surgery). Keywords: acute appendicitis, acute complicated appendicitis, acute uncomplicated appendicitis, surgery, paediatric patients, leucine-rich alpha-2 glycoprotein 1 (LRG1), neutrophil gelatinase-associated lipocalin (NGAL), interleukin-6 (IL-6), Escherichia coli, Pseudomonas aeruginosa, Yersinia enterocolitica. This research received grant support from the Latvian Council of Science and Rīga Stradiņš University.
