Endocrine Abstracts

Nadir growth hormone (GH) levels after oral glucose tolerance test (OGTT) as well as random insulin-like growth-factor I (IGF-I) levels, given as multiples of the upper limit of normal [xULN], were used to evaluate biochemical activitiy of acromegalic patients. The development of new, more sensitive GH assays makes it necessary to reevaluate the cut off values of the GH nadir after OGTT.

In a cross sectional study, we evaluated nadir GH concentrations during OGTT and IGF-I levels before glucose load in a series of 66 acromegalic patients (31f/35 m, median age 53 y (range 20–75)). 56 of the 66 patients underwent surgery, 13 were irradiated. 25 patients were on medication (somatostatin analogue or dopamine agonist). GH levels were measured 3 h following glucose (75 g) administration. Concentrations of GH and IGF-I were determined by a single lab using the same chemiluminescence immunoassays.

45 patients had an xULN≤1 (normal IGF-I). 25/45 patients had nadir GH-levels ≤0.3 μg/L, whereas 20/45 patients showed nadir GH levels ranging from 0.4–3.6 μg/L (11: 0.4–1.0 μg/L, 9: 1.1–3.6 μg/L,). All 21 patients who’s xULN exceeded 1 had a nadir GH-level>0.3 μg/L. (7: 0.4–1.0 μg/L, 14>1.0 μg/L). In the 7 patients with a GH nadir between 0.4–1.0 μg/L and an xULN>1, median xULN was 1.43 (range 1.10–1.82).

In our series, all patients with a GH nadir ≤0.3 μg/L showed normal IGF-I reflecting complete biochemical remission. All patients with an xULN>1 also had a GH nadir>0.3 μg/L. Patients with a GH nadir of 0.4–1.0 μg/L may have a higher risk of relaps (xULN≤1) or the possibility that a small residual activity of acromegaly persists (xULN>1).