Endocrine Abstracts

Introduction: The usefulness of acute octreotide suppression test (OST) in the selection of patients with acromegaly for chronic somatostatin analogues (SA) treatment is still controversial.

Aim: To investigate the predictive value of OST for long-term responsiveness to long-acting SA.

Materials and methods: Retrospective study of 25 drug-naive patients (13 males) with active acromegaly, subjected to an OST (hourly serum GH concentrations for 8 h were measured before and after last administration of S.C. octreotide 100 μg q8 h for 48 h). The mean achieved GH was used for analysis. GH nadir response during OST was also evaluated. GH<1 ng/ml and normal IGF1 (both evaluated as mean of three values) were used as parameters for biochemical control during SA therapy.

Results: On average, during OST a GH decline of 70.15±23.4% was observed in this cohort. Most patients (72%; n=18) showed a decrease > 50% of GH during OST (group A), while 28% had ≤50% GH reduction (group B). During SA treatment, 61.1% of group A achieved IFG1 and/or GH normalization, with a mean reduction of 54.6 and 68.2% respectively. In Group B, 28.5% reached IFG1 and/or GH normalization, with a mean reduction of 42 and 52.7%, respectively. Biochemical control was observed in 11.1% of patients on group A and 14.3% on group B. In total, 36% of patients achieved a GH value<1 ng/ml during the OST. In this group 77.8% (n=7) had mean reduction >50% during OST. This test showed positive (PPV) and negative predictive (PNV) values of 64.71 and 71.43% for 50% GH reduction and PPV (66.67%) and PNV (56.25%) for minimal GH level<1 ng/ml during OST. A 50% reduction and a nadir GH<1 ng/ml during OST didn’t show correlation with the long-term normalisation of serum IGF1 and/or GH (P=0.106 and P=0.271 respectively).

Conclusion: In this cohort, a reduction of 50% and nadir GH<1 ng/ml following an OST weren’t predictive of remission on long-term SA as defined by updated criteria.