The value of the oral glucose tolerance test, random serum growth hormone and mean growth hormone levels in assessing the postoperative outcome of patients with acromegaly

P>Background The nadir GH value following an oral glucose tolerance test (OGTT) and the mean GH levels obtained from a GH day curve (GHDC) are among the tools currently used for assessing therapeutic end-points in surgically treated acromegaly. The latter test, however, is cumbersome and costly. Objectives To evaluate, by using a modern, two-site chemiluminescent immunometric GH assay, the degree of discordance between the nadir GH following an OGTT and the mean GH obtained from a GHDC after surgical treatment of acromegaly and to check whether the OGTT can replace reliably the GHDC for the assessment of the disease status postoperatively. Patients and methods Forty-nine patients [25 males/24 females, median age 52 years (range 18-70)] with a GH-secreting pituitary adenoma who had been surgically treated previously underwent hormonal evaluation of their disease status. The GHDC comprised of 9 x 30-min samples for GH collected in the morning after an overnight fast and rest. Results Seven per cent of patients with mean GH < 1 center dot 7 mu g/l (5 mU/l) in the GHDC had nadir GH > 0 center dot 7 mu g/l (2 mU/l) in the OGTT, and 10% of those with mean GH > 1 center dot 7 mu g/l had nadir GH < 0 center dot 7 mu g/l in the OGTT (all cases with discrepancies had normal IGF-I). GH value at time 0 min < 0 center dot 6 mu g/l in the OGTT had positive predictive value 100% and negative predictive value 75% in predicting nadir GH < 0 center dot 3 mu g/l (1 mU/l) in the OGTT. Nadir GH < 0 center dot 8 mu g/l in the OGTT had positive predictive value 97% and negative predictive value 95% in predicting mean GH < 1 center dot 7 mu g/l in the GHDC. Mean GH in the OGTT < 1 center dot 4 mu g/l had a positive predictive value 90% and negative predictive value 95% in predicting mean GH < 1 center dot 7 mu g/l in the GHDC. Mean GH in the OGTT < 2 center dot 5 mu g/l had positive predictive value 100% and negative predictive value 81% in predicting normal IGF-I. GH at time 0 min in the GHDC < 2 center dot 1 mu g/l had positive predictive value 90% and negative predictive value 90% in predicting mean GH < 1 center dot 7 mu g/l in the GHDC. Conclusions The hormonal data obtained from an OGTT (mean and nadir GH) can provide comprehensive information on the status of acromegaly following surgery and can replace the GHDC cost-effectively. Furthermore, a morning fasting GH sample has an excellent positive predictive value in predicting biochemical cure and an optimal prognostic profile in predicting safe mean GH levels.