Value of early postoperative random growth hormone levels and nadir growth hormone levels after oral glucose tolerance testing in acromegaly

OBJECTIVE: There is no ideal marker to identify residual tumor tissue after surgery in patients with acromegaly. The purpose was to elucidate if early postoperative hormone testing gives reliable information regarding complete resection of a GH-producing pituitary adenoma.

DESIGN: Fourty-eight patients undergoing surgery for acromegaly from 04/2013-05/2014 were prospectively examined for random GH, IGF1, and GH levels after oral glucose tolerance testing (OGTT) in the early postoperative phase and on follow-up. Criterion for inclusion was a minimum follow-up of one year for each patient with respect to remission.

RESULTS: Thirty-three patients showed GH suppression below 1 μg/l after OGTT in the early postoperative phase. Follow-up GH, IGF1 and OGTT tests confirmed the initial findings in 30 patients. The three remaining patients showed biochemical signs of persisting acromegaly. In the remaining 15 patients early postoperative GH suppression was above 1 μg/l. Of those, six patients went into remission during follow-up, nine patients without postoperative GH suppression <1 μg/l remained acromegalic.

CONCLUSIONS: GH suppression to <1 μg/l as well as random GH levels below 1 μg/l in the early postoperative phase seem to be of good positive predictive value for long-term remission. However, several patients without suppression of GH to <1 μg/l in the early postoperative OGTT went into delayed remission. These results have to be taken into account prior to initiation of further therapy.