Circulating eosinophil cell-free DNA as a noninvasive biomarker for perforated appendicitis in pediatric patients-a proof-of-concept study.

Appendicitis is the most common condition necessitating emergency abdominal surgery. While most cases are localized, 20% become complicated, resulting in perforation. The management of non-complicated appendicitis varies across medical centers, encompassing both surgical and non-surgical options, whereas complicated appendicitis is predominantly managed surgically. Differentiating them is clinically challenging, especially in pediatric patients, crucial for guiding appropriate treatment strategies. Therefore, there is an unmet need for biomarkers to distinguish the two entities. Here we examined the utility of epigenetic liquid biopsies in appendicitis. We used DNA methylation markers specific to immune and gastrointestinal epithelial cells to assess the tissue origins of plasma cell-free DNA (cfDNA) in appendicitis patients. Appendix epithelium cfDNA was undetected in plasma samples from children with appendicitis relative to control groups. In contrast, neutrophil and regulatory T-cell cfDNA were elevated in appendicitis enhancing the specificity and sensitivity of appendicitis diagnosis beyond the information provided by neutrophil counts. Notably, eosinophil cfDNA was most significantly elevated in children with perforated compared with non-perforated appendicitis. This finding was cross-validated using a machine-learning approach. In conclusion, eosinophil cfDNA levels are elevated in children with a perforated appendix and may have potential as a non-invasive aid in diagnosing perforated appendicitis in the future.