Periostin and KIM-1 as Fibrosis-Related Markers Associated with CKD Stage in Children

Early diagnosis of chronic kidney disease (CKD) remains a major clinical challenge. Periostin (POST) and kidney injury molecule-1 (KIM-1) have been proposed as biomarkers of tubular injury and fibrosis. This study aimed to evaluate their utility as markers associated with CKD stage and their associations with renal function and proteinuria in children. Twenty-three children with CKD stages I–IV and 23 healthy controls were enrolled. Serum and urinary POST and KIM-1 were measured together with creatinine (CR), cystatin C (CysC), proteinuria, albuminuria, and urinary α1- and β2-microglobulin. Patients were classified as early stage (ES; CKD I–II) or late stage (LS; CKD III–IV). Serum and urinary POST and KIM-1, uPOST/CR, uKIM-1/CR, fractional excretion indices (FePOST, FeKIM-1), and UPCR were higher in CKD patients than in controls. Absolute biomarker concentrations did not differ between ES and LS and were not associated with eGFR, UPCR, UACR, or tubular protein excretion. In contrast, uPOST/CR, uKIM-1/CR, FePOST, and FeKIM-1 increased with CKD stage, were higher in LS than ES, correlated positively with CysC, and inversely with eGFR. FePOST and FeKIM-1 also correlated strongly with tubular protein markers. The FePOST/FeKIM-1 ratio was elevated in ES patients compared with controls and remained stable across CKD stages. Fractional excretion of POST and KIM-1 is associated with CKD stage and reflects ongoing tubular injury in children. The FePOST/FeKIM-1 ratio may represent a sensitive marker of early CKD.