Objective: Retesting of adolescents with childhood-onset GH deficiency (GHD) is recommended, but age-related reference data are scarce. We aimed to establish a cut-off value for the GHRH-arginine test (GHRH+ARG) at the typical age of retesting at near-adult height.
Designs: We retrospectively studied 149 patients (108 males) with childhood-onset GHD aged 16.8 ± 1.7 years (mean ± SD) with a BMI of 20.9 ± 3.5 kg/m(2) who had received GHRH+ARG in one single center during 8 consecutive years. Based on the IGF-I serum concentration falling below -2 SDS when off GH, 22 patients suffered from severe GHD of adulthood while 122 were GH sufficient. Five patients could not be determined definitively. GH and IGF-I were measured by in-house RIAs. IGF-I values were transformed into age-related SDS values. ROC-analysis was used to determine the cut-off value.
Results: For GHRH+ARG, a cut-off limit of 15.9 ng/ml had the highest pair of sensitivity (91%) and specificity (88%). GH peaks of the patients with a normal BMI between -1 and 0 SDS were higher than those with a high BMI >1 SDS (p<0.01).
Conclusions: When retesting adolescents at near-adult height for severe GHD of adulthood, a GH value of <15.9 ng/ml in GHRH+ARG is discriminatory with good accuracy. Conversion factors for other GH assays in use are provided. A rational decision for or against the continuation of GH therapy into adulthood can be made based on the clinical history of the patient and the combination of the GHRH+ARG retest result and the IGF-I serum concentrations when off GH.
Keywords: BMI; Childhood-onset GHD; GH cut-off; GHRH–arginine test; IGF-I.
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