6379 Clonidin does not stimulate copeptin release

Abstract Disclosure: G. Binder: None. K. Weber: None. A. Peter: None. R. Schweizer: None. Background: Copeptin is secreted in isomolar amounts along with arginine vasopressin peptide from the posterior pituitary. Its stability makes it a perfect candidate for a biomarker of AVP deficiency. In children, the infusion of arginine and bolus of insulin stimulate copeptin; the respective stimulation test could be an alternative to the water deprivation test. Here, we retrospectively studied the effect of clonidine on copeptin release. Design and patients: This is a monocentric retrospective analysis of donated residual serum samples from 42 children with suspected of GH deficiency who underwent clonidine stimulation between 2020 and 2023. Measurements: Copeptin was measured in baseline, 30-, 60-, 90- and 120-min samples by BRAHMS Copeptin proAVP Kryptor immunofluorescence assay. GH was measured using an in-house RIA calibrated against the WHO International Reference Preparation 98/574. Results: According to the test results (clonidine and arginine test), there were 20 patients with GHD and 16 without GHD. No patient had polyuria-polydipsia syndrome. Median age was 6.7 years (quartiles; 5.6-7.8), the median height was -2.92 SDS (-3.42- -2.34), and the median BMI was-0.29 SDS (-1,32 - +0,16). The median baseline level of copeptin was 5,6 pmol/l (3.4-9.6). Median copeptin mildly decreased to 4.5 pmol/l (3.0-10.0) after 30 min; this change was not significant (P=0.45). Thereafter, median values remained low at 4.6, 4.6 and 4.6 pmol/l (60, 90 and 120 min). There was no correlation between baseline copeptin levels and the diagnosis of GHD. Conclusion: The clonidine stimulation test does not stimulate copeptin release and is therefore not suitable for the assessment of AVP deficiency in children. Presentation: 6/2/2024