Alexopoulou O et al. (2008) Divergence between growth hormone and insulin-like growth factor-1 concentration in the follow-up of acromegaly. J Clin Endocrinol Metab [doi:10.1210/jc.2007-2104]

Biochemical control of acromegaly in noncured patients is usually defined as serum growth hormone (GH) levels <2.0 µg/l, plus normal-for-age serum levels of insulin-like growth factor I (IGF-I). Alexopoulou et al., however, have confirmed reports of discordant IGF-I and GH results in noncured patients with acromegaly: in over one-third of their cohort, one parameter was elevated despite the other being normal.

The Belgian Acromegaly Register provided data on 229 patients (mean age ± SD 54 ± 14 years; 124 men) with noncured acromegaly. Serum IGF-I and GH levels were measured by validated assays. In total, 81 patients had active disease (IGF-I and GH both high), 68 patients had biochemically controlled disease (IGF-I and GH both normal), and 80 patients had discordant results (25 had elevated GH only, and 55 had elevated IGF-I only). Notably, the high-GH phenotype was most frequent in young, nonirradiated, estrogen-sufficient women, which could indicate roles for age, sex and radiotherapy in IGF-I–GH discordance. The high-IGF-I phenotype was twice as common as the high-GH phenotype, and was associated with a notably poor metabolic profile; the authors concluded that high IGF-I might indicate persistently active disease even when mean GH values lie in the normal range.

The authors infer that constant peripheral exposure to even slightly elevated GH levels might be sufficient to raise IGF-I levels above normal, and suggest that different GH threshold values might be needed to monitor acromegaly in estrogen-exposed patients.