All are true about hypernatremia due to diarrhoea except

Notably, osmotic diarrhoea and viral gastroenteritis typically generate stools with Na+ and K+ <100 mM, thus leading to water loss and hypernatremia; in contrast, secretory diarrhoea typically results in isotonic stool and thus hypovolemia with or without hypovolemic hyponatremia. The appropriate response to hypernatremia and a serum osmolality >295 mOsm/kg is an increase in circulating AVP and the excretion of low volumes (<500 mL/d) of maximally concentrated urine, i.e., urine with osmolality >800 mOsm/kg; should this be the case, then an extrarenal source of water loss is primarily responsible for the generation of hypernatremia. (as in diarrhoea) Ref: Harrison 19e pg: 304