An unresponsive 76-year-old male is admitted to the intensive care unit. He has a past medical history of bipolar affective disorder (treated with lithium and valproate), self-harm and previous suicide attempts.
His bloods show an acute on chronic kidney injury with polyuria (100-330ml/hr) and an eGFR of 15. Serum sodium is 165mmol/L. Plasma and urine osmolalities were measured:
Plasma osmolality – 356 mOsmol/kg
Urine osmolality – 231 mOsmol/kg
