Endocrine Abstracts

Introduction: The benefits of growth hormone (rGH) replacement during the transition from childhood to adulthood are well established. In adulthood rGH dose is optimized by titrating to serum IGF-I concentration. The use of non-specific IGF-I reference ranges may result in erroneous assessment of IGF-I concentration and inappropriate rGH dosing.

Methods: IGF-I methods and reference ranges across 9 UK centres were reviewed. Immulite IGF-1 results for a 12 month period following initiation of adult dose rGH replacement were recorded in patients aged 15–25 treated in our institution over the past 7 years. Oestrogen medication status was noted. Adequacy of rGH dose was compared to Immulite based IGF-1 results from an age- and sex- matched Danish cohort, and using two current, but different, reference ranges.

Results: Only 1/9 UK centres used both age and gender specific reference range up to 20 years of age, and different ranges were in place even when using the same assay. IGF-I data were available for 30 local patients (20 female, 10 male). 14/20 females were on oestrogen replacement. Whilst only 1/30 IGF-1 results fell below one reference range, 7/30 were below the second. Results from 8/30 patients (all female) fell below 2 standard deviations from the mean result derived from the reference cohort (P<0.05). Conclusions. Different IGF-1 reference ranges are use in the UK. In this study female transition patients were under-treated with rGH when compared to the reference cohort. As a new IGF-1 international standard is available (02/254) if should be possible to harmonize age and gender specific IGF-1 reference ranges. Unfortunately assays calibrated to this standard are not currently in widespread use. As well as the use of inappropriate reference ranges serum IGF-1 concentration has large intra- and inter-individual variability, and is dependent upon multiple variables; this should also be considered when reviewing IGF-I results.

Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.