A GH peak of 3 μg/l during the insulin tolerance test (ITT) is considered the gold standard for identifying adults with severe GH deficiency. Alternative stimuli such as arginine (AST) and glucagon (GST) are also employed but produce lower GH peaks than the ITT in normal subjects. Despite this, 3 μg/l is used as the diagnostic threshold for these tests, raising the possibility that severe GH deficiency is being diagnosed inappropriately.
We studied 4584 patients enrolled in KIMS (3070 underwent an ITT, 1320 an AST and 910 a GST at diagnosis) to determine whether these patients exhibited a similar phenotype. Interquartile ranges of GH peaks achieved during the ITT were determined (1st <0.12, 2nd 0.130.39, 3rd 0.40.99, 4th 1.03.0 μg/l). These limits were applied to the AST and GST. Comparisons were made in the 1st and 4th quartiles between the AST vs ITT and GST vs ITT for the following clinical variables: BMI, IGF-I SDS, cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, waist:hip ratio and quality of life (QoL-AGHDA). quartile. AST vs ITT: BMI was higher (30.6 vs 28.8 kg/m2, P<0.0001) in the AST group. GST vs ITT: IGF-I SDS was lower (-1.9 vs -2.8, P=0.003), HDL was higher (1.1 vs 1.2 mmol/l, P=0.025) and triglycerides were lower (2.7 vs 2.3 mmol/l, P=0.003) in the ITT group. quartile. AST vs ITT: BMI was higher in the AST group (29.0 vs 28.0 kg/m2, P=0.035). GST vs ITT: Quality of life was worse in the GST group (15 vs 12, P<0.0001).
None of the other parameters was significantly affected in either quartile.
Using a diagnostic threshold of 3 μg/l, the AST and GST identified GHD patients with similar features to those defined by the ITT. This is reassuring for future studies on the impact of GH replacement in the KIMS database.
03 - 07 May 2008
European Society of Endocrinology