Influence of BMI and Menstrual Cycle on Growth Hormone Nadir Following Oral Glucose Load in Premenopausal Women
Presentation Number: SUN 435
Date of Presentation: April 2nd, 2017
Katharina Schilbach*, Andreas Lechner, Michael Haenelt, Christina Gar, Rita Schwaiger and Martin Bidlingmaier
Klinikum der Universität München, München, Germany
Growth hormone (GH) suppression following oral glucose load (oGTT) is the gold standard test in diagnosis of acromegaly. To rule out active acromegaly, GH nadirs < 1 ng/mL and < 0.4 ng/mL, have been suggested, respectively, without further differentiation for gender, age or hormonal status. In addition, discrepancies between GH nadir and IGF-I have been described with increasing incidence and have triggered search for factors modifying GH suppression. In view of modern, sensitive GH-assays calibrated against the recombinant standard, further adjustment of the GH nadir seems to be required to increase the sensitivity of diagnosing acromegaly.
We aimed to establish GH nadir cut-offs for a GH assay calibrated against the new recombinant standard and, specifically, measuring the 22kD GH isoform (IDS-iSYS). Here we present data for healthy premenopausal women with normal age- and gender-adjusted IGF-I (n=301). We analyzed the impact of age, body mass index (BMI), menstrual cycle, oral contraceptive use (OC), insulin sensitivity (IS) and gestational diabetes (GDM) during previous pregnancies.
GH nadirs following oral glucose (75 g) intake were < 0.4 ng/mL in > 95% of the women (80% < 0.2 ng/mL; 50% <0.1 ng/mL). BMI was the major determinant, with lower GH nadirs in subjects with higher BMI. In 4 different BMI groups (A: < 20 kg/m2, n=28, B: 20-25 kg/m2, n=152, C: 25-30 kg/m2, n=66 and D: > 30 kg/m2, n=53) mean GH nadirs were as follows: A: 0.24 ng/mL, B: 0.15 ng/mL, C: 0.10 ng/mL and D: 0.08 ng/mL with significant differences between all groups except group C vs. D (A vs. B: p<0.05, A vs. C p<0.001, A vs. D <0.001 and B vs. C: p<0.001). In line with this finding, women with reduced insulin sensitivity index (ISI, n=93) and women with GDM requiring insulin therapy (n=113) had significantly lower GH nadirs (p<0.001 for both groups). In contrast to some earlier reports, in our study phases of the menstrual cycle did not significantly influence GH nadir (mean): early follicular phase (n=57, GH nadir 0.12 ng/mL), late follicular phase (n=31, GH nadir 0.12 ng/mL), luteal phase (n=63, GH nadir 0.15 ng/mL) and periovulatory phase (n=14, GH nadir 0.14 ng/mL), p>0.9 between all groups.
Our findings suggest that, in premenopausal females, cut-offs for GH nadir need to be lowered if new sensitive hGH assays are used. Based on our results in healthy premenopausal females, we suggest cut-offs of 0.5, 0.4, 0.3 and 0.2 ng/mL for BMIs < 20 kg/m², 20-25 kg/m², 25-30 kg/m² and > 30 kg/m², respectively. Phases of menstrual cycle do not impact the nadir values.
Nothing to Disclose: KS, AL, MH, CG, RS, MB