Cut-off limits of the GH response to GHRH plus arginine test and IGF-I levels for the diagnosis of GH deficiency in late adolescents and young adults

Objective: To define the appropriate diagnostic cut-off limits for the GH response to GHRH + arginine (ARG) test and IGF-I levels, using receiver operating characteristics (ROC) curve analysis, in late adolescents and young adults. Design and methods: We studied 152 patients with childhood-onset organic hypothalamic-pituitary disease (85 males, age (mean ± S.E.M.): 19.2 ± 0.2 years) and 201 normal adolescents as controls (96 males, age: 20.7 ± 0.2 years). Patients were divided into three subgroups on the basis of the number of the other pituitary hormone deficits, excluding GH deficiency (GHD): subgroup A consisted of 35 panhypopituitary patients (17 males, age: 21.2 ± 0.4 years), subgroup B consisted of 18 patients with only one or with no more than two pituitary hormone deficits (7 males, age: 20.2 ± 0.9 years); and subgroup C consisted of 99 patients without any known hormonal pituitary deficits (60 males, age: 18.2 ± 0.2 years). Both patients and controls were lean (body mass index, BMI < 25 kg/m²). Patients in subgroup A were assumed to be GHD, whereas in patients belonging to subgroups B and C the presence of GHD had to be verified. Results: For the GHRH + ARG test, the best pair of highest sensitivity (Se; 100%) and specificity (Sp; 97%) was found choosing a peak GH of 19.0 μg/l. For IGF-I levels, the best pair of highest Se (96.6%) and Sp (74.6%) was found using a cut-off point of 160 μg/l (SDS: - 1.3). Assuming 19.0 μg/l to be the cut-off point established for GHRH + ARG test, 72.2% of patients in subgroup B and 39.4% in subgroup C were defined as GHD. In patients belonging to group B and C and with a peak GH response < 19 μg/I to the test, IGF-I levels were lower than 160 μg/I (or less than 1.3 SDS) in 68.7 and 41.6% of patients respectively predicting severe GHD in 85.7% of panhypopituitary patients (subgroup A). Conclusions: In late adolescent and early adulthood patients, a GH cut-off limit using the GHRH + ARG test lower than 19.0 μg/l is able to discriminate patients with a suspicion of GHD and does not vary from infancy to early adulthood.