Growth Hormone Related Diseases and Therapy by Ken Ho

Author:Ken Ho
Language: eng
Format: epub
Publisher: Humana Press, Totowa, NJ

In recent years, the GHRH-AST has been identified as a robust alternative to the ITT in the diagnosis of adult GHD. The utility of the GHRH-AST in 62 patients with CO GHD in late adolescence and young adulthood has been studied and a peak GH cut-off of <10 mcg/L has been identified during two provocative tests [64]. Using a peak GH cut-off of <9 mcg/L (first centile), 94% of those with idiopathic GHD with other pituitary hormone deficits and/or structural abnormalities and 52% of those with idiopathic isolated GHD and no structural abnormalities have been identified, all patients with a peak GH <9 mcg/L during a GHRH-AST also had a peak GH of <3 mcg/L during an ITT [64]. There is a growing recognition that GH response during provocative testing is reduced with increasing BMI, evidence from GHRH-AST studies in adults [65–67], and has led to reducing peak GH cut-offs being recommended for increasing levels of BMI by the GH Research Society [54, 55].

In certain groups of patients with GHD in childhood, a normal response to a GHRH-AST may be misleading. A study comparing ITT with GHRH  +  AST in adult survivors of brain tumours and leukaemia showed that, within 5 years of cranial irradiation, there was a reduction in peak GH response observed during an ITT and not during a GHRH  +  AST, whereas after a longer duration the discordancy between the two tests reduced [68]. Therefore, a normal response to a GHRH-AST in a patient with CO GHD which is potentially secondary to hypothalamic dysfunction, for instance, secondary to cranial irradiation, does not exclude GHD.

Recently, availability of GHRH has been limited and therefore alternatives to the ITT and GHRH-AST have been sought. In adults, the GST is as specific and sensitive as the ITT at identifying severe GHD with a lower peak GH cut-off of 3 mcg/L [69, 70]. The AST with a peak GH cut-off of <0.4 mcg/L is also an alternative with a sensitivity of 87% and specificity of 91% [71]. Validation is required of both the GST and AST in CO GHD in late adolescence. Other pharmacological stimuli are not recommended.

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