Background: IgA vasculitis (IgAV) represents the most frequently seen form of vasculitis among children. Although it often resolves without intervention, renal involvement (IgAV nephritis) poses a risk for long-term complications. Although the lectin and alternative complement pathways are possible causes in its development, dependable serum biomarkers for the early identification of nephritis remain unavailable. Methods: In this prospective case-control study, we examined how the serum levels of a membrane attack complex (sC5b-9), complement factor H (CFH), mannose-binding lectin (MBL), and mannose-binding lectin-associated serine protease-1 (MASP-1) relate to renal involvement in IgAV. These complement proteins were measured in children diagnosed with IgAV and compared to levels in healthy controls (HCs) matched for age and sex. Results: The study cohort comprised 44 IgAV patients with a median age of 8 years and 34 HCs. The CFH levels were reduced significantly in the patient group (median: 357.31 ng/mL; IQR: 228.32) relative to the controls (median: 543.08 ng/mL; IQR: 504.05) (p < 0.001). This decrease was observed irrespective of the presence of nephritis. There were no significant differences in serum sC5b-9, MBL, or MASP-1 levels between the patients and controls. Furthermore, no correlation emerged between these complement components and renal involvement. Conclusion: The data suggest that lower CFH levels may signal systemic dysregulation of the alternative pathway in IgAV. In contrast, the serum levels of sC5b-9, MBL, and MASP-1 appear inadequate as markers for predicting renal involvement. Further research with larger cohorts that includes genetic analyses and examination of kidney tissue is needed to better define the contribution of complement activation in IgAV-related nephritis.

Background/Objectives: This study aimed to evaluate the correlation of mid-upper arm circumference (MUAC) z-scores with body mass index (BMI) and weight-for-height (WFH) z-scores to determine its reliability in identifying malnutrition and its potential in clinical practice in healthy children and adolescents. Methods: Our study included 906 healthy children and adolescents aged between 2 months and 18 years who were admitted to University Hospital’s General Pediatrics Clinic and attended 12 primary schools in 6 additional Izmir provinces. Anthropometric measurements (weight, length/standing height, MUAC, BMI, WFH) were performed. The relationship between MUAC z-scores, BMI, and WFH z-scores of cases with malnutrition were evaluated. Results: According to the WHO BMI z-score classification, 6 (0.7%) of the children were defined as having severe undernutrition, 43 (4.7%) as moderate undernutrition, 146 (16.1%) as mild undernutrition, 486 (53.6%) as normal, 142 (15.7%) as overweight, and 83 (9.2%) as obese. At any age over two years, fair agreement was observed between MUAC z-scores and WHO BMI z-scores in defining malnutrition alone compared to other growth measures (weighted kappa = 0.371). Under two years of age, the correlation between MUAC z-scores and BMI z-scores showed moderate agreement in detecting overweight and obesity (weighted kappa = 0.479), and between MUAC and WHO WFH z-scores showed moderate agreement (kappa = 0.252). Conclusions: The study found a moderate and fair connection between MUAC z-scores and other criteria. However, further MUAC z-score screening and diagnostic power testing in larger pediatric populations are needed to validate its use alongside other key anthropometric indicators in malnutrition diagnosis. MUAC measurement should be popularized in routine pediatric outpatient clinics to detect malnutrition quickly.