Do impaired glucose tolerance and diabetes mellitus interfere with the interpretation of the growth hormone response to the oral glucose tolerance test?

1. The ability of glucose to suppress growth hormone (GH) secretion is well known and the glucose test is widely used for the diagnosis of acromegaly. However, when suspected acromegaly is associated with diabetes mellitus (DM) or impaired glucose tolerance (IGT) the interpretation of the GH response to the oral glucose tolerance test (OGTT) may be difficult. Recently, Hattori et al. (Journal of Clinical Endocrinology and Metabolism, 70: 771-778, 1990), using a highly sensitive (1.5 ng/l) polyclonal antibody-based immunoenzymometric assay, found no differences in the GH response to glucose load among control, IGT and DM patients. 2. We employed a less sensitive (100 ng/l) but monoclonal antibody-based immunoenzymometric assay to measure the serum GH levels of 19 normal subjects, 11 patients with DM and 11 patients with IGT to determine the effect of glucose intolerance on the GH response to the OGTT. 3. Complete suppression of GH (< 0.1 microgram/l) was achieved in 73% of the controls with a mean nadir of 0.17 +/- 0.16 microgram/l (range, < 0.1-0.6 microgram/l). GH was completely suppressed in 82% of the diabetics with a mean nadir of 0.58 +/- 1.21 micrograms/l (range, < 0.1-4.0 micrograms/l). However, complete suppression occurred in only 27% of the IGT patients with a nadir of 1.09 +/- 2.08 micrograms/l (range, < 0.1-7.0 micrograms/l), which was statistically higher than observed for controls and diabetics. 4. We conclude that plasma GH levels after glucose loading of IGT patients should be interpreted with caution because an abnormal response can be detected when some sensitive immunometric assays are employed.