Over the past 15 yr it has been established that circulating GH continues to have important biologic functions in regulating body composition, psychologic health, exercise performance, and aspects of intermediary metabolism in the adult. Many well-designed studies have shown that GH deficiency results in adverse effects on these variables, and that these abnormalities can be largely corrected by GH replacement (43). Although expensive, most Western countries have now approved recombinant human GH for use in the adult with severe hypopituitarism.
Not all subjects with GH deficiency have significant symptoms. In treated pituitary tumor patients, those with complaints relating to poor quality of life, altered body composition, with documented dyslipidemia or reduced bone mineral density, should undergo assessment for GH deficiency (Table 2). Severe GH deficiency has been defined as a peak GH response on provocative testing <9 mU/L (3.5 ^g/L) and GH has a license for use in this group. The insulin-hypoglycemia test (see Appendix 1, p. 197) is the gold standard. In most patients, two tests of GH reserve are required and a dynamic test is usually combined with a GH day-curve and measurement of serum total IGF-1. Recombinant GH is manufactured by several companies and is often in the form of a powder for reconstitution before injection using a multidose pen device. A ready-to-use liquid form has recently been developed. Patients are taught to self-administer subcutaneous injections, usually at bedtime. Most centers advocate initiation of a small dose with regular clinical assessments and measurement of IGF-1 to ensure individual dose titration to minimize adverse effects (44).
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