A 75-year-old male presents
with lethargy and dizziness on standing. He gives a history of having had
treatment for tuberculosis when he was young.
On examination he looks
underweight, his skin is pigmented and there is pigmentation of his buccal
mucosa and pigmentation of the palmar creases. His nipples and areola are
pigmented. There is no vitiligo. His blood pressure is 120/70 lying down and
90/60 on standing.
His blood urea 10.3 mmol/L,
Na 120 mmol/L, K 5.9 mmol/L
Which of the following
investigations is most likely to identify the aetiology of his condition?
0900 ACTH level
Short synacthen test
Long ACTH stimulation test
Serum aldosterone /plasma renin activity