A 56-year-old male presents with a history of feeling
tired and weak. On examination he is obese and has marked pigmentation of his
skin. Blood pressure 190/110. he also has demonstrable weakness of his
proximal muscles .
Urea 5 mmol/L
Sodium 140 mmol/L
Potassium 2.7 mmol/L
Bicarbonate 32 mmol/L
Glucose 12 mmol /L
In this patient which one of the following would you
arrange as the initial investigation?
24 hour urinary free cortisol
High dose dexamethasone suppression test
Plasma ACTH levels