IGF-I measurements in the monitoring of GH therapy.

Growth hormone replacement therapy has been used regularly in adult Growth hormone deficiency since the availability of recombinant GH in the 1980's. GH replacement improves quality of life, bone turnover markers, cardiovascular risk markers and adverse body composition. Originally, GH doses in replacement regimes were determined by weight and surface area and dose increases based on body composition outcomes analogous to pediatric practice. These regimens led to significant side effects related to excess GH, arthralgias, headaches and peripheral edema and IGF-I levels above the upper limit of the reference range. Newer treatment regimes therefore account for known factors affecting serum GH and IGF-I levels, i.e. age, gender, estrogen replacement and pre-treatment IGF-I levels. Monitoring is now via clinical symptomatology combined with serum total IGF-I levels, potentially this avoids excessive GH exposure and allows monitoring of compliance and dose titration. There is a lack of data relating IGF-I to biological endpoints, but analysis suggests that dose titration of IGF-I to the upper half of the age and gender related reference range is acceptable. The use of reliable IGF-I assays and extensive age and gender related reference ranges is necessary and centralized monitoring is preferable. Free IGF-I and bioavailable IGF-I measurements are available but their use in the monitoring of GH replacement remains to be determined.