Physiologic Approach to Hypotonic Hyponatremia The next time you have a case of hypotonic hyponatremia, give the physiologic approach a try. It can be easier to remember than the normal volume-based algorithm Urine Na+K / serum Na >1 is predictive of poor response to volume restriction alone in SIADH RAAS Inactive or Ineffective (UNa >30) • ADH Present (Uosm ≥100): SIADH, Renal Sodium loss (diuretics, mineralocorticoid deficiency, Post-AKI diuresis can be high or low Uosm), Hypothyroidism, Adrenal Insufficiency, Cerebral Salt Wasting • ADH Not Present (Uosm <100): Renal Losses (AKI, Post-AKI diuresis) RAAS Active (or too little relative solute intake, UNa <20) • ADH Present (Uosm ≥100): Hypovolemia, Hypervolemia with poor renal perfusion (Heart failure, Cirrhosis, Nephrotic syndrome) • ADH Not Present (Uosm <100): Excessive Free water intake (Primary polydipsia), Low solute intake (Beer potomania, malnutrition), Reset Osmostat Stanford Internal Medicine Chiefs @StanfordChiefs #Physiologic #Hypotonic #Hyponatremia #differential #diagnosis #table #sodium #nephrology
