Dehydration and Polyuria

🗒️ Question

A 68 year old man is brought to the emergency department with confusion, fatigue and a history of polyuria over the past week. He has type 2 diabetes managed with metformin. His family reports he has been unable to drink adequate fluids.

On examination, he is drowsy and poorly responsive. His blood pressure is 90/55 mmHg, pulse rate is 105 bpm and regular, and his mucous membranes are dry. He has reduced skin turgor and delayed capillary refill.

Investigations:

• Blood glucose: 40 mmol/L (4.0–7.8 mmol/L)

• Serum osmolality: 330 mOsm/kg (275–295 mOsm/kg)

• Ketones: 0.2 mmol/L (<0.6 mmol/L)

• Arterial blood gas: pH 7.38 (7.35–7.45)

What is the most appropriate initial investigation?

(A) Serum osmolality

(B) Urinary ketones

(C) Arterial blood gas

(D) Serum electrolytes

(E) Blood cultures