Rare causes of acute hyperkalemia in the 1st week of life. Three case reports.

We describe three neonates with hyperkalemia and renal salt wasting during the 1st week of life. Endocrinological evaluation led to the diagnosis of selective hypoaldosteronism (HA) in two neonates and secondary pseudohypoaldosteronism (PHA) in one. The infant with PHA developed a urinary tract infection, and radiological investigation demonstrated a small dysplastic left kidney with vesicoureteral reflux. The electrolyte and hormonal disturbances in this infant persisted throughout the first months of life. The two infants with selective HA improved rapidly after administration of fludrocortisone orally and the electrolytes and renin values returned to normal. Secondary PHA and selective HA should be considered in the differential diagnosis in salt-losing neonates during the first days of life. Renal ultrasonography, urine culture, and assays of aldosterone and plasma renin activity should be performed in any infant presenting with hyperkalemia and salt wasting after the exclusion of congenital adrenal hyperplasia.