Discordant Nadir GH After Oral Glucose and IGF-I Levels on Treated Acromegaly: Refining the Biochemical Markers of Mild Disease Activity

Abstract

Biochemical markers for remission on acromegaly activity are controversial. We studied a subset of treated acromegalic patients with discordant nadir GH levels after oral glucose tolerance test (oGTT) and IGF-I values to refine the current consensus on acromegaly remission. We also compared GH results by two GH immunoassays. From a cohort of 75 treated acromegalic patients, we studied 13 patients who presented an elevated IGF-I despite post-oGTT nadir GH of ≤1 μg/l. The 12-h daytime GH profile (GH-12 h), nadir GH after oGTT, and basal IGF-I levels were studied in patients and controls. Bland-Altman method showed high concordance between GH assays. Acromegalic patients showed higher mean GH-12 h values (0.71±0.36 vs. 0.31±0.28 μg/l; p<0.05) and nadir GH after oGTT (0.48±0.32 vs. 0.097±0.002 μg/l; p<0.05) as compared to controls. Nadir GH correlated with mean GH-12 h (r=0.92, p<0.05). The mean GH-12 h value from upper 95% CI of controls (0.54 μg/l) would correspond to a theoretical normal nadir GH of ≤0.27 μg/l. Patients with GH nadir ≤0.3 μg/l had IGF-I between 100–130% ULNR (percentage of upper limit of normal range) and mean GH-12 h of 0.35±0.15, and patients with GH nadir >0.3 and ≤1 μg/l had IGF-I >130% ULNR and mean GH-12 h of 0.93±0.24 μg/l. Our data integrate daytime GH secretion, nadir GH after oGTT, and plasma IGF-I concentrations showing a continuum of mild residual activity in a subgroup of treated acromegaly with nadir GH values ≤1 μg/l. The degree of increased IGF-I levels and nadir GH after oGTT are correlated with the subtle abnormalities of daytime GH secretion.

Key words

acromegaly - GH - IGF-I

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