Influence of gender, age, body mass index, abdominal fat and serum levels (HDL-C, glucose, triglycerides, IGF-1) on growth hormone (GH) response to GH-releasing hormone plus arginine and insulin tolerance tests / Einfluss von Geschlecht, Lebensalter, BMI, Bauchumfang und laborchemischen Parametern (HDL-C, Glukose, Triglyzeride, IGF-1) auf den Wachstumshormon-Anstieg nach der Durchführung eines GHRH+Arginin- und eines Insulin-Toleranz-Tests
Authors: Fedeler Eva , Spilcke-Liss Elisabeth , Schroeder Henry W.S. , Lerch Markus M. , Nauck Matthias , Friedrich Nele , Wallaschofski Henri 
Published: February 2010

Background: Diagnosis of growth hormone (GH) deficiency in adulthood is established by provocative testing of GH secretion. The insulin tolerance test (ITT) is recommended as the gold standard, whereas the combined GH-releasing hormone (GHRH) plus arginine (GHRH+ARG) test is considered the best alternative to the ITT. The aim of the present study was to correlate the degree of the GH response to the GHRH+ARG test and to the ITT and to assess the influence of gender, age, body mass index (BMI), abdominal circumference, high-density lipoprotein cholesterol (HDL-C), triglycerides, serum glucose and insulin-like growth factor 1 (IGF-1) to the GH response.

Methods: A total of 50 adult patients (25 men, 25 women) aged 18–74 years were studied. BMI and abdominal circumference were measured. Basal blood samples were taken for IGF-1, HDL, glucose and triglycerides. All subjects underwent GH provocation with both the GHRH+ARG test and the ITT.

Results: Peak GH response was significantly higher (men/women: p<0.01) after GHRH+ARG than with ITT, with a strong positive correlation between the peak GH responses in both tests (r=0.753, p<0.01). Peak GH response to ITT and to GHRH+ARG was significantly higher in females than in males (ITT, p=0.01; GHRH+ARG, p<0.01). A significant negative correlation was found between the peak GH response after ITT and GHRH+ARG and age (ITT, r=−0.322; GHRH+ARG, r=−0.281). There was also a significant negative correlation between peak GH response to GHRH+ARG and BMI (r=−0.332) and abdominal circumference (r=−0.388). Peak GH response was positively correlated with plasma IGF-I levels in both tests (ITT, r=0.437; GHRH+ARG, r=0.346). On the basis of the GH response to both GH provocation tests, the subjects were divided into two groups: group 1, subjects with severe GH deficiency (23 patients with GH peak ≤3 μg/L in ITT and ≤9 μg/L in GHRH+ARG); group 2, subjects with slight or without GH deficiency (27 subjects with GH peak >3 μg/L in ITT and >9 μg/L in GHRH+ARG). In group 1 patients, plasma IGF-I concentrations were lower than in group 2 (p=0.019) and there were significantly older (p=0.042) and more male (p=0.0041) patients in group 1. No significant difference was found for BMI, abdominal circumference, HDL, glucose and triglyceride levels between the two groups.

Conclusions: The results of the present study indicate that the degree of the GH response to ITT and GHRH+ARG is correlated with age and plasma IGF-I levels. There is a correlation between peak GH after GHRH+ARG and BMI as well as abdominal circumference. Therefore, age-, gender- and BMI-related test specific cut-off points are required.