Our results indicate that the hyponatremia observed in MIS-C patients (mean value = 134.94 mmol/L) is likely driven by inappropriate ADH secretion, leading to SIADH, as demonstrated by the elevated urinary-to-plasma osmolality ratio (mean value U/P ratio = 1.92) and high urinary osmolality in these patients (mean value = 539.68 mOsm/kg). Here, AVP is linked to inappropriate ADH syndrome.