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Postoperative Evaluation of Patients with Acromegaly: Clinical Significance and Timing of Oral Glucose Tolerance Testing and Measurement of (Free) Insulin-Like Growth Factor I, Acid-Labile Subunit, and Growth Hormone-Binding Protein Levels

Division of Endocrinology (R.A.F., J.A.M.J.L.J., P.U., L.J.H., S.W.J.L., A.J.v.d.L., W.W.d.H.), Department of Internal Medicine, Erasmus Medical Center, 3015 GD Rotterdam, The Netherlands; Neuroendocrine Unit (M.B.), Innenstadt University Hospital, 80336 Munich, Germany; and Division of Clinical Endocrinology (C.J.S.), Department of Medicine, Charite Campus Mitte, 10117 Berlin, Germany

Address all correspondence and requests for reprints to: R. A. Feelders, M.D., Ph.D., Erasmus Medical Center Rotterdam, Department of Internal Medicine, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. E-mail: r.feelders{at}erasmusmc.nl.

Context: It is not exactly known when patients with acromegaly should be evaluated for cure after transsphenoidal adenomectomy (TA).

Objective: The objective of this study was to define the optimal time point of postoperative evaluation by serial measurements of glucose-suppressed GH levels [oral glucose tolerance test (OGTT)] and the GH-dependent parameters IGF-I, free IGF-I, acid labile subunit (ALS), and GH-binding protein (GHBP).

Design: We describe a prospective study with 1-yr follow-up.

Setting: The study was conducted at a university hospital.

Patients: Seventeen patients with acromegaly were included in the study.

Main Outcome Measures: The main outcome measures were OGTT results at 1, 2, 3, 8, and 12 wk after TA; weekly measured GH, (free) IGF-I, ALS, and GHBP levels up to 12 wk; and total IGF-I levels measured at 52 wk.

Results: Postoperatively, nine patients were in remission with an OGTT GH nadir of less than 0.5 µg/liter and normalized IGF-I levels, whereas eight patients had persistent acromegaly. In both cured and noncured patients, OGTT results at 1 wk after TA were highly reproducible over time. In contrast, early postoperative IGF-I levels fluctuated and only stabilized at 12 wk. In all cured patients, free IGF-I levels rapidly normalized within 2 wk after TA (specificity, 100%). Preoperative ALS levels were elevated in all patients and normalized only in the cured patients after TA (specificity, 89%). Preoperative GHBP levels were low and increased from 2 wk after surgery.

Conclusions: We show that in the postoperative evaluation of patients with acromegaly, already 1 wk after surgery, an OGTT using 0.5 µg as the GH nadir cutoff value has a high predictive value for cure, whereas early IGF-I levels show varying patterns toward stabilization. Therefore, IGF-I should be measured as a predictive parameter not within 3 months after surgery. Free IGF-I and ALS levels may have an additional value in the postoperative assessment of disease activity.

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