Predicting long-term remission by measuring immediate postoperative growth hormone levels and oral glucose tolerance test in acromegaly

BACKGROUND: The suppression of the growth hormone (GH) on an oral glucose tolerance test (OGTT) has been accepted as the most reliable parameter for determining remission of acromegaly. OBJECTIVE: To evaluate the role of immediate postoperative GH level and 1-week postoperative OGTT as early predictive tools of long-term surgical remission. METHODS: One hundred ninety-four acromegalic patients who received transsphenoidal tumor resection and were followed up for > 1.5 years (3.80 ± 0.17 years) with at least 3 postoperative OGTTs were evaluated. Level of GH was measured 2, 6, 12, 18, 24, 48, and 72 hours postoperatively, and an OGTT was performed 1 week after surgery, every 6 months for the first 3 years, and annually thereafter. RESULTS: One hundred seventy-seven patients underwent gross total resection; long-term remission was achieved in 153. The GH level at 24 hours after surgery showed the highest predictive power for long-term remission. Long-term remission was maintained in 125/127 (98.4%) patients who had nadir GH levels < 1.0 μg/L on an early postoperative OGTT. However, when nadir GH levels were > 1.0 μg/L on an early postoperative OGTT, long-term remission was observed in 28 patients (28 of 67, 41.8%) in a delayed fashion. One-week postoperative OGTT had a sensitivity of 81.7% and specificity of 95.1% for predicting remission. CONCLUSION: Immediate postoperative GH level is a very good predictor of long-term outcome in acromegaly. One-week postoperative OGTT is also a good predictor with high specificity. These findings may provide critical information for the determination of adjuvant treatment after surgery.