Plasma Copeptin in Response to Oral Urea in Healthy Adults and Patients With Polyuria-polydipsia Syndrome

"Diagnostic test with a single weight-adapted dose of oral urea dissolved in 200 ml water together with 5 g of lemon-lime flavor powder (containing maltodextrin and citric acid).~The investigators will make use of the lemon-lime flavor to soften the bitter taste of urea.~\- Dose calculation: 0.5 g urea/kg body weight (rounded to no decimal places), with a minimal dose of 30g and a maximal dose of 45g."

"Diagnostic test with a single weight-adapted dose of placebo dissolved in 200 ml water together with 5 g of lemon-lime flavor powder (containing maltodextrin and citric acid).~The placebo will contain a mixture of bitter herbal substances to mimic the taste of urea.~\- Dose calculation: 22 ml of placebo containing 20 ml Ergytonyl®, 1 ml Carmol®, and 1 ml Bitter Liebe®."