Basal GH levels are elevated and fluctuate widely but do not correlate well with any clinical manifestation of the disease. GH stimulates the production of insulin-like growth factor I (IGF-I) and levels of IGF-I are often, though not invariably, elevated in acromegaly (Fig. 3.14).
In normal subjects, GH levels are mostly undetectable in the serum, apart from intermittent pulses of secretion, lasting approximately ninety minutes, which occur five or six times during the day and more frequently at night. This pulsatile nature of GH secretion in normal subjects means that it may not be possible to distinguish between normal and some acromegalic patients using basal GH concentrations; dynamic tests are therefore necessary.
