Letter regarding "Serum gelsolin as a biomarker for differentiating familial Mediterranean fever from juvenile idiopathic arthritis in children".

Dişçi et al. reported promising discrimination between familial Mediterranean fever (FMF) and juvenile idiopathic arthritis (JIA) using serum gelsolin (Gsn), achieving an area under the receiver operating characteristic curve of 0.82. However, the performance observed in small, selected groups of children with established diagnoses may not generalize to patients presenting with diagnostic uncertainty. Deriving and evaluating the diagnostic threshold within the same cohort, without independent validation, may lead to overly optimistic estimates of sensitivity and specificity. Furthermore, the incremental diagnostic value of Gsn beyond standard clinical assessment and routine laboratory markers remains unclear. To determine if Gsn offers clinically useful information for differentiating FMF from JIA, prospective studies are needed. These studies should enroll consecutive children with diagnostic uncertainty, utilize prespecified thresholds, and include independent validation.