Evaluation of the GHRH–arginine retest for young adolescents with childhood-onset GH deficiency

Abstract

ObjectiveRetesting 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. DesignsWe retrospectively studied 149 patients (108 males) with childhood-onset GHD aged 16.8±1.7years (mean±SD) with a BMI of 20.9±3.5kg/m2 who had received GHRH+ARG in one single center during 8consecutiveyears. 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. ResultsFor GHRH+ARG, a cut-off limit of 15.9ng/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). ConclusionsWhen retesting adolescents at near-adult height for severe GHD of adulthood, a GH value of <15.9ng/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.