Taner Adıgüzel, Erdin Kalyoncuoğlu, Gülsüm Kaya
Background: We compared biochemical, micronutrient-related and complete blood count (CBC)-derived inflammatory profiles among children with obesity, undernutrition and normal weight, and explored the discriminatory performance of selected routine laboratory markers for the obesity phenotype. Methods: In this single-centre retrospective comparative study, medical records of children aged 2-17 years evaluated between January 2023 and December 2025 were reviewed. Participants were classified as obese, undernourished or normal weight using World Health Organization (WHO) body mass index-for-age (BMI-for-age) references. Liver enzymes, lipid parameters, iron-related indices, micronutrient levels, zinc, insulin and CBC-derived inflammatory indices were compared across groups using non-parametric omnibus tests. Exploratory receiver operating characteristic (ROC) analyses were performed for selected markers. Results: A total of 690 children were included: 100 with obesity, 90 with undernutrition and 500 with normal weight. The obesity group was significantly older than the normal-weight group (median 11.0 vs. 7.5 years; p < 0.001). Obesity was characterised by higher alanine aminotransferase (ALT), insulin, triglycerides, neutrophil-to-lymphocyte ratio (NLR), systemic immune-inflammation index (SII) and systemic inflammation response index (SIRI), together with lower high-density lipoprotein (HDL) cholesterol, 25-hydroxyvitamin D [25(OH)D] and aspartate aminotransferase-to-alanine aminotransferase (AST/ALT) ratio (all p < 0.05). In exploratory, age-unadjusted ROC analyses, the AST/ALT ratio yielded the highest AUC among the evaluated biomarkers (AUC 0.859; 95% CI 0.823-0.895; optimal cut-off ≤ 1.52; sensitivity 77.0%; specificity 77.6%), followed by SIRI (AUC 0.751; 95% CI 0.700-0.802). Conclusions: Pediatric obesity was associated with a distinct liver enzyme-metabolic-inflammatory laboratory profile, whereas undernutrition exhibited a different micronutrient-biochemical pattern. Because the study was retrospective and age-unadjusted, these findings should be interpreted as exploratory and hypothesis-generating. Prospective studies with age-balanced sampling, pubertal staging and liver imaging are required before clinical implementation.