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

Abstract

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 (OGTT(100) ) and 75 g glucose (OGTT(75) ) 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. To compare both tests in acromegalic patients and to evaluate test reproducibility with respect to gender. OGTT(100) and OGTT(75) were performed on two consecutive days in 54 acromegalic patients (46·9 ± 1·8 years, 30 women). OGTT(75) was repeated on three different occasions in 11 healthy men and 13 healthy women at different phases of the menstrual cycle. GH nadirs were comparable between tests [2·40 ± 0·52 (OGTT(100) ) and 2·46 ± 0·54 μg/l (OGTT(75) ); 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 OGTT(100) and OGTT(75) [area under the receiver operated curve (ROC) = 0·995]. In men, GH, insulin and glucose measurements during OGTT(75) were highly reproducible. In women, however, basal and GH nadirs were significantly higher midcycle (P < 0·05). In acromegalic patients, there is no difference in GH nadirs and test interpretation after the ingestion of 100 g or 75 g glucose. The OGTT(75) is highly reproducible in men, but in women, it should be performed preferably in the early follicular phase.