Hyponatremia Diagnosis and Management in Elderly Patients

Introduction to Hyponatremia

The American Geriatrics Society recommends measuring serum osmolality directly to exclude pseudohyponatremia and determine if the patient is truly hypo-osmolar, with a threshold of <280 mOsm/kg 1
The European Society of Clinical Nutrition suggests checking serum glucose and urea to ensure they are within normal range, as elevated levels can falsely elevate osmolality and must be normalized before interpretation 1, 2

The American College of Physicians recommends obtaining a spot urine sample for osmolality measurement when serum osmolality is confirmed <280 mOsm/kg, and interpreting urine osmolality in context, with <100 mOsm/kg indicating primary polydipsia 1
The Clinical Nutrition Society suggests measuring urine sodium on the same sample as urine osmolality for proper interpretation, with urine sodium <20 mmol/L suggesting hypovolemic hyponatremia, and urine sodium >40 mmol/L suggesting SIADH or renal/endocrine causes 1, 2

The American Academy of Family Physicians recommends limiting correction of hyponatremia to <10-12 mEq/L per 24 hours to prevent osmotic demyelination syndrome 4
The European Society of Clinical Nutrition suggests considering volume depletion and low-intake dehydration as distinct entities, with urine osmolality useful only for the former when evaluating hyponatremia, not the latter 1, 5

The American Geriatrics Society recommends checking for unmeasured osmoles, such as ethanol, mannitol, and glycine, that can interfere with osmolality interpretation and obscure the diagnosis 1
The Clinical Nutrition Society suggests avoiding reliance on single urine osmolality measurements in patients with fever or critical illness, as non-osmotic ADH stimulation can cause hourly fluctuations 1, 2