Reliability of the oral glucose tolerance test in the early postoperative assessment of acromegaly remission.

OBJECT: The suppression of growth hormone (GH) to less than 1 microg/L during the oral glucose tolerance test (OGTT) is generally considered to be the standard for the assessment of biochemical remission of GH excess following surgery for GH-secreting pituitary adenomas. In this study the authors examine the reliability of the results of the early postoperative OGTT (epOGTT) in indicating remission or persistence of active acromegaly.
METHODS: Data from the case files of 67 consecutive patients who underwent surgery for the first time for GH-secreting pituitary adenomas were reviewed retrospectively. Definitive remission of acromegaly was considered to be present if, without adjuvant therapy and at the most recent follow-up examination, GH was suppressed to less than 1 microg/L during the OGTT, the level of insulin-like growth factor-I (IGF-I) was within normal limits, and there was no clinical or magnetic resonance imaging evidence of persisting disease. The results of the epOGTT (obtained during the 2nd postoperative week) and the 3-month-postoperative OGTT (3mpOGTT) were compared with the patient's outcome at the most recent follow-up examination. A highly sensitive (< or = 0.3 microg/L) immunoradiometric assay for GH and a highly sensitive (< or = 32 microg/L) radioimmunoassay for IGF-I were used. Correct epOGTT findings were noted in 83.6% of the patients: correct normal results (definitive remission of acromegaly) in 55.2% and correct pathological results (persisting acromegaly) in 28.3% of the patients. The rate of false findings was 16.4%: false normal results in 1.5% and false pathological results in 14.9% of the patients. The rate of correct 3mpOGTT findings increased to 98.5%: correct normal results in 68.6% and correct pathological ones in 29.8% of the patients. A false (false pathological) 3pmOGTT result occurred in only one patient (1.5%). At the most recent follow-up examinations (median 3.6 years) all OGTT findings were correct: correct normal results in 70.1% and correct pathological results in 29.9% of the patients. An intact adenopituitary function was associated (p = 0.04) with the occurrence of false epOGTT findings.
CONCLUSIONS: The high rate of false results, 16.4% for the epOGTT, declined significantly to 1.5% 3 months postoperatively and to 0% at the most recent follow-up examination. The OGTT appears to be more reliable at 3 months postoperatively. Unless there is obvious evidence of persisting disease following surgery for GH-secreting pituitary adenomas, adjuvant therapy should be delayed for 3 months postoperatively to avoid subjecting the patient to superfluous treatment.