Comparison of oral glucose tolerance test (OGTT) 100 g with OGTT 75 g for evaluation of acromegalic patients and the impact of gender on test reproducibility

Summary Context Growth hormone (GH) measurements during an oral glucose tolerance test (OGTT) are essential for the diagnosis and follow‐up management of acromegaly. However, both 100 g glucose (OGTT100) and 75 g glucose (OGTT75) test variants are in clinical use. Whether the tests are interchangeable concerning GH nadir and test interpretation is unclear. Furthermore, information on test reproducibility and the impact of gender is scarce. Objective To compare both tests in acromegalic patients and to evaluate test reproducibility with respect to gender. Design, subjects and methods OGTT100 and OGTT75 were performed on two consecutive days in 54 acromegalic patients (46·9 ± 1·8 years, 30 women). OGTT75 was repeated on three different occasions in 11 healthy men and 13 healthy women at different phases of the menstrual cycle. Results GH nadirs were comparable between tests [2·40 ± 0·52 (OGTT100) and 2·46 ± 0·54 μg/l (OGTT75); P = 0·356]. There were no differences at any time point in the mean values of GH, serum glucose or insulin between the two test variants. Test interpretation was highly consistent between the OGTT100 and OGTT75 [area under the receiver operated curve (ROC) = 0·995]. In men, GH, insulin and glucose measurements during OGTT75 were highly reproducible. In women, however, basal and GH nadirs were significantly higher midcycle (P