RT Journal Article SR Electronic T1 PP-020 The effect of substitution of vitamin D in children under growth hormone therapy – absolute deficiency JF BMJ Paediatrics Open JO BMJ Paediatrics Open FD BMJ Publishing Group Ltd SP A73 OP A73 DO 10.1136/bmjpo-2024-EPAC.164 VO 8 IS Suppl 5 A1 Hasanbegovic, Snijezana A1 Tihic-Kapidzic, Suzana A1 Begovic, Ermin A1 Hasanbegovic, Snijezana YR 2024 UL http://bmjpaedsopen.bmj.com/content/8/Suppl_5/A73.2.abstract AB Aim Vitamin D and growth hormone (GH) are synergists in creating healthy, strong and adequately long bones. Vitamin D deficiency is present in up to 80% of children. To compare the average growth in body height in the first year of GH therapy in pediatric patients with GH deficiency without and with adequate vitamin D substitution.Material and Method The diagnosis of absolute deficiency of GH was established by a stimulation test with insulin hypoglycemia with a cut-off value of 10 µg/L. In the first group, vitamin D was not administered or substituted before the start of GH therapy, and in the second vitamin D was determined by the immunoassay method of patients and substituted to reference values (>30 ng/ml) before the start of GH therapy.Results The average dose of GH for both groups was 0.034 mg/kg/day. GH therapy was started immediately for 28 patients (15M/13F), the average increase in height after first year of therapy was 10.5 cm. In the second group of patients 31 (17M/14F), only 20% of the children had vitamin D in the reference range, and the mean was 14.9 ng/ml, after 2 months D vitamin it was substituted to mean of 39 ng/ml and GH was started. The average height increase in body height in the first year of therapy for this group was 11.9 cm (p < 0.05).Conclusions Before the start of HR therapy, determining the level of vitamin D and substituting it in a short time to the reference values is important fot a significantly greater increase in body height in the first year of growth hormone therapy in patients with absolute deficiency and achieving better results of therapy in general.