A 33-year-old man complains of a tingling sensation in his hands for several months which occasionally awakens him during sleep. The patient has noticed he has gained weight and no longer wears his wedding ring as it has become too tight. You notice the patient is sweating while speaking to you and has quite a large jaw, furrowed tongue and large hands. His blood pressure reading is 142/91 mmHg. The most appropriate investigation would be:

The glucose tolerance test (B) is diagnostic in patients with suspected acromegaly, many of whom will appear diabetic. Growth hormone (GH) Levels (C) can be raised during periods of stress and for most of the time remain <1 mU/L. A raised GH level is therefore not sufficient to diagnose acromegaly though low or undetectable level can exclude this diagnosis. An MRI scan (A) is the best modality to reveal a pituitary adenoma secreting GH, however this investigation should always follow an abnormal glucose tolerance test reading. Hyperprolactinaemia (D) is commonly associated in acromegaly patients as the pituitary adenoma often co-secretes GH and prolactin and is useful to measure in a confirmed diagnosis of acromegaly and especially if a patient presents with symptoms of elevated prolactin.