GH Use in the Transition of Adolescence to Adulthood

The achievement of final adult height occurs much earlier than the acquisition of peak bone mass and muscle strength in both genders, males achieving these milestones later than females. This transition period is particularly challenging in adolescents that were treated with GH during childhood. A high percentage of these adolescents in transition are no longer considered GH-deficient at the completion of their linear growth, making it necessary to retest GH reserves using potent secretagogues (such as insulin tolerance tests (ITT) or arginine/GHRH) and more stringent cutoff peaks (<6 ng/ml in this age group for ITT for example) to establish the correct diagnosis of GH deficiency. This is especially important in those with idiopathic isolated GH deficiency. Who, how and when to test are critical so that patients who are truly GH-deficient can be selected for lifelong therapy while others are spared. Data on the efficacy of GH in these patients have shown mixed results (some positive changes, others minimal or no improvement) on body composition and bone mineral density (BMD) accrual, e.g., most likely due to the differences in the length of time that patients have been off GH in the published studies. In those persistently deficient with abnormally low BMD (i.e. <-2 SD), low IGF-1 and abnormal body composition (high % body fat), GH should be continued starting at doses of 12.5 microg/kg x day and IGF-1 measured periodically and kept in the mid to upper limits of normal (within +1 SD). A repeat DEXA scan for BMD and body composition assessment a year after initiation of treatment is useful to guide therapy. GH is no substitute for healthy eating, weight control and regular exercise in diminishing cardiovascular risk, but these subjects should likely be treated at least through their mid-20s when peak BMD and muscle strength are achieved, at which time reassessment of the lifelong need for GH can be made in the idiopathic GH-deficient group. Those with multiple pituitary hormone deficiencies on the other hand should be replaced indefinitely with GH. The treatment of the GH-deficient adolescent in transition should be individualized.