21st May 2025

You are asked to review a 75-year-old lady with a sodium of 113 mmol/L as she has become acutely confused, with vomiting and diarrhoea.

You are asked to review a 75-year-old lady with a sodium of 113 mmol/L as she has become acutely confused, with vomiting and diarrhoea. She has a background of stage 2 CKD. On assessment she is tachycardic at 120bpm and her blood pressure is 105/80. The rest of her observations are within normal range. Serum osmolality is 240 mOsmol/kg. Urine sodium is 10 mmol/L. She is hypovolaemic on examination.

Which of the following causes would most likely account for the hyponatraemia? Please select only ONE answer.