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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

¹ Endocrinology, Department of Clinical and Experimental Medicine, ‘Amedeo Avogadro’ University of Novara, Via Solaroli, 17, 28100 Novara, Italy² Division of Pediatrics,, ‘Amedeo Avogadro’ University of Novara, 28100 Novara, Italy³ Department of Endocrinology,, ‘Federico II’ University of Naples, 80100 Naples, Italy⁴ Division of Endocrinology and Metabolic Diseases,, University of Turin, 10100 Turin, Italy⁵ Endocrinology Service,, Regina Elena Cancer Institute, 00100 Rome, Italy⁶ Division of Pediatric Endocrinology,, Hospital of Treviglio, 24047 Treviglio, Italy⁷ Department of Pediatrics,, IRCCS G. Gaslini, University of Genoa, 16100 Genoa, Italy⁸ Division of Pediatrics,, University of Parma, 8100 Parma, Italy⁹ Eli-Lilly,, Florence, Italy and ¹⁰ Division of Pediatrics,, ‘Federico II’ University of Naples, Naples, Italy

(Correspondence should be addressed to G Aimaretti; Email: gianluca.aimaretti{at}med.unipmn.it)

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/l to the test, IGF-I levels were lower than 160 µg/l (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.