What is the most appropriate next step in management?

A 46-year-old South Asian man presented with a 2-month history of dry mouth and polyuria. He had hypertension treated with bendroflumethiazide. There was no family history of diabetes mellitus, but his father had died suddenly during lower limb angioplasty at the age of 51.

On examination, the patient’s pulse was 76 beats per minute and regular, and his blood pressure was 164/86 mmHg. The rest of the physical examination was normal. Urinalysis was normal.

Investigations:

serum sodium143 mmol/L (137C144)

serum potassium3.0 mmol/L (3.5C4.9)

serum creatinine123 µmol/L (60C110)

fasting plasma glucose6.9 mmol/L (3.0C6.0)

What is the most appropriate next step in management?
A . change bendroflumethiazide to ramipril
B . haemoglobin A1c measurement
C . oral glucose tolerance test
D . repeat fasting plasma glucose
E . start oral hypoglycaemic treatment