Endocrine Abstracts

Introduction: Discordance between growth hormone (GH) and insulin-like growth factor 1 (IGF1) is observed in up to 30% patients with acromegaly, with the most common finding being high IGF1 with normal GH levels. Recently published guidelines recommended a nadir GH of 0.4 μg/L rather than 1.0 during growth hormone suppression test as being indicative of controlled disease. This may lead to reduced discordance between GH and IGF1. Methods We measured nadir GH (Beckman Coulter Ultrasensitive assay) during a growth hormone suppression test and IGF1 (Siemens Immulite 1000 assay) in all patients with acromegaly attending our clinic. Patients were defined as having a high nadir GH if nadir GH was ≥ 0.4 μg/L. IGF1 was defined as high if above the age and gender related reference range. Medical therapy for acromegaly was obtained from clinical records. We excluded patients diagnosed in previous six months or with pituitary surgery or irradiation in the previous six months.

Results: Using GH nadir of <0.4 μg/L, 16/52 patients (30.7%) showed discordance between GH and IGF1. 2 (3.8%) patients demonstrated elevated IGF1 despite a suppressed nadir GH. However 14 (26.9%) patients showed elevated nadir GH despite a normal IGF1. Using the older cut-off of nadir GH of <1.0 μg/L, discordance was again high in 14 (26.9%) patients, with 11 (21.1%) having a normal nadir GH and high IGF1, while only 3 patients (5.7%) elevated GH and normal IGF1. We found no relationship between discordance and medical therapy (dopamine agonist or somatostatin analogue).

Conclusions: Despite the recent recommendation of a lower nadir GH level during a growth hormone suppression test, our results show similar rates of discordance as reported previously, but with the most common finding now being elevated GH and normal IGF1.

Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.