The investigations in acromegaly should include:
- insulin-like growth factor 1 levels:
- a better test than growth hormone levels because IGF-1 levels are less variable
- also raised in pregnancy and puberty
- failure of growth hormone to be suppressed by 75 g oral glucose - false positive tests occur in poorly controlled diabetes mellitus, anorexia nervosa, hypothyroidism, Cushing's
- MRI / CT scan may reveal pituitary adenoma
- chest and abdominal radiology:
- to detect an ectopic source of growth hormone
- may detect cardiomegaly due to cardiomyopathy
- hands radiology reveals:
- tufting of terminal phalanges
- increased joint spaces due to cartilage hypertrophy
- assessment of pituitary function
- calcium - hypercalciuria is common in acromegaly due to a direct renal tubular action of growth hormone; if there is moderate or severe hypercalcaemia then this is suggestive of hyperparathyroidism (MEN-I)
- phosphate is often raised
Note that isolated GH measurement may show raised levels - however random levels are not diagnostic because levels vary with the time of day and other factors.