Saltwasting

Saltwasting is a clinical syndrome characterized by excessive loss of sodium in the urine, which can lead to hyponatremia, hypovolemia, and dehydration. It may result from defects in kidney tubule reabsorption or from hormonal disturbances that reduce sodium conservation.

Renal causes include inherited tubulopathies such as Bartter syndrome and Gitelman syndrome. Bartter syndrome involves a defect in the thick ascending limb Na-K-2Cl transporter, producing a loop diuretic–like effect with renal salt loss, hypokalemia, and metabolic alkalosis, often presenting in infancy. Gitelman syndrome results from a defect in the distal tubule Na-Cl cotransporter and typically shows milder salt loss with hypokalemia and often hypomagnesemia.

Hormonal causes include congenital adrenal hyperplasia due to 21-hydroxylase deficiency, in which aldosterone production is impaired, leading to salt-wasting crises in newborns with hyponatremia, hyperkalemia, dehydration, and hypotension. Acquired adrenal insufficiency can produce similar findings. In some cases, extensive gastrointestinal losses from conditions such as severe diarrhea or vomiting can mimic saltwasting, though these are extrarenal.

Diagnosis rests on clinical history and laboratory findings. Blood tests reveal hyponatremia and signs of volume depletion; urine studies show high sodium loss. Hormonal assays (renin and aldosterone) help differentiate renal from adrenal causes.

Treatment focuses on correcting volume and electrolyte deficits and addressing the underlying cause. In congenital adrenal disorders, mineralocorticoid replacement and salt supplementation are essential. In renal tubulopathies, management includes ongoing electrolyte replacement and, for Bartter syndrome, sometimes medications to reduce urinary losses. Prognosis depends on the underlying condition and the timeliness of treatment.