A  
Hyponatremia, hyperkalemia and metabolic acidosis in a vomiting neonate indicate a salt-wasting adrenal crisis, the typical presentation of 21-hydroxylase–deficient congenital adrenal hyperplasia rather than pyloric stenosis (classically alkalotic), renal failure, or galactosemia [Rohrer, 2003, PMID 12566686; Ferraz Liz, 2021, PMID 30855422].