Endocrine Abstracts

Introduction: Polyuria polydipsia is a common paediatric presentation. The water deprivation test (WDT) is the gold standard to differentiate arginine vasopressin (AVP) deficiency (central diabetes insipidus, CDI), from habitual drinking. However, it burdens patients, families, and clinical staff significantly. Copeptin, which is co-secreted in equimolar amounts with AVP, can be easily measured by a simple blood test. There have been advances in using copeptin in diagnosing AVP deficiency (CDI) in adults, but data in children remain limited.

Methods: We performed a single-centre, retrospective study of children and young people (CYP) who underwent WDT between December 2019 and February 2024. Copeptin levels were obtained at baseline and every 2 to 3 hours during WDTs.

Results: 17 patients were included (11 males and 6 females). The median age was 7 years (age range between 2 to 15 years). In >95% of these patients, the primary reason for referral was a history of polyuria and polydipsia. Three patients were diagnosed with AVP deficiency based on their plasma and urine osmolality values. It was excluded in 13 patients, while the results were inconclusive in 1 patient. Copeptin levels in those diagnosed with AVP deficiency were <2.0 pmol/l at baseline and with an average maximum of 2.5 pmol/l by the end of the test. CYP with normal response to WDT had an average copeptin level of 5.3 pmol/l at the baseline and an average maximum of 10 pmol/l at the end of the test.

Conclusions: Basal copeptin levels ≥5 pmol/l could be used to exclude AVP deficiency (CDI) in CYP, whilst basal copeptin <2 pmol/l are highly suggestive of AVP deficiency (CDI). We suggest WDT can be safely avoided in these instances. Copeptin levels between 2-5 pmol/l would necessitate a WDT to rule out AVP deficiency (CDI). We suggest the above cutoffs would help reduce the burden of WDTs. However, a large, prospective multi-centre study is needed to confirm our observation and cutoff values.