Acute kidney injury in a 78-year-old woman with recent gastroenteritis and new NSAID use

Judy is a 78-year-old woman with a history of hypertension and osteoarthritis. She presents to the emergency department with a 24-hour history of nausea, vomiting, and decreased urine output. She also complains of weakness and lightheadedness on standing.

Three days before admission, she had a short episode of diarrhoea and vomiting, which she attributed to gastroenteritis. Since then, she has been unable to eat or drink much.

Her regular medications include lisinopril 10 mg once daily, bendroflumethiazide 2.5 mg once daily, and amlodipine 5 mg once daily. Five days ago, a general practitioner prescribed ibuprofen 400 mg three times daily for knee pain. She has been taking it regularly. She also takes paracetamol 500 mg occasionally, about one or two tablets per week.

On examination, she is alert but drowsy. Blood pressure is 96/58 mmHg, pulse 110 beats per minute and regular. Temperature is 36.8°C. Her mucous membranes are dry, and skin turgor is reduced. Heart sounds are normal, chest is clear. There is mild tenderness over the left knee, but no swelling.

Initial blood tests: creatinine 245 micromol/L (baseline 85 micromol/L), urea 21.5 mmol/L, sodium 136 mmol/L, potassium 5.2 mmol/L, bicarbonate 18 mmol/L. Estimated GFR is 16 mL/min/1.73 m². Haemoglobin 132 g/L, white cell count 8.9 x 10⁹/L. Urinalysis shows no blood, no protein, and no casts. Urine biochemistry shows sodium 12 mmol/L, fractional excretion of sodium 0.8%. Renal ultrasound shows two normal-sized kidneys with no obstruction.