THU171 Reference Intervals For Bioavailable IGF-I Values In Dutch Healthy Children, Adolescents And Young Adults

Disclosure: K. Pellikaan: None. M. Elizabeth: None. A.C. Hokken-Koelega: None. S.A. van den Berg: None. L. de Graaff-Herder: None. Background: Immunoreactive ‘total’ IGF-I is the main biochemical marker for titration of growth hormone (GH) treatment. However, in several endocrine disorders like Prader-Willi syndrome (PWS) and Silver-Russell syndrome, total IGF-I levels are often higher than expected based on GH dose and clinical effects. When patients reach total IGF-I concentrations above +2SDS, fear of negative long-term effects makes clinicians reduce GH dose. This dose reduction often leads to a deterioration in body composition, growth (in children) and quality of life, which suggests that bioavailability of IGF-I is reduced in patients with these disorders. Measurement of bioavailable IGF-I could improve GH dose titration. However, use of bioavailable IGF-I assays has been hindered by the lack of proper reference intervals. We report reference intervals of bioavailable IGF-I in a large group of healthy children, adolescents and adults. Methods: Serum was collected of 260 Dutch healthy controls aged 1-21 years. Total IGF-I and unbound, bioavailable IGF-I were measured manually using Ansh Labs total and free IGF-I assays. We calculated male and female age-related reference intervals for total and bioavailable IGF-I. Results: We present male and female age-related reference intervals. Both total and bioavailable IGF-I increased with age and were significantly higher in females than in males (p < 0.001). Conclusions: the reported reference intervals for bioavailable IGF-I concentrations will facilitate the use of bioavailable IGF-I levels as an alternative marker for GH dose titration in patients with disorders in which total IGF-I levels are unreliable. Presentation: Thursday, June 15, 2023