Arginin-stimulated Copeptin in Polyuria-polydipsia Syndrome in Children

"Copeptin test is performed after solid fasting since midnight without water restriction. After blood collection on heparin tube used for biological inclusion criteria, heparinized plasma is transferred to Timone University hospital (transport temperature +4°C) for screening copeptin assay.~The basal copeptin level determines the next step:~1. copeptin ≥ 30 pmol/L defines the diagnosis of NDI and results in a specific care;~2. copeptin \< 30 pmol/L defines the group of eligible patients for arginine stimulation"

The arginine-stimulated copeptin test start at 8 am, after solid fasting since midnight without water restriction, and 30 min of rest in decubitus position. A dose of 0.5 g/kg of arginine (maximum 40g) diluted in 0.9% NaCl is infused over 30 min through a peripheral venous line. Copeptin is measured at T0 (before infusion), T45, T60, T90, and T120 min after infusion.

"Based on our previous study, patients with basal copeptin value over 3.53 pmol/L are considered as positive diagnosis of PP (Se 100%, Sp 87.4%) and cerebral MRI is not performed for this group of patients (PP group).~A cerebral and pituitary MRI performed according to reference procedures (without and with contrast medium used in routine care) for patients considered as an uncertain diagnosis (UD) based on basal copeptin value (\< 3.53 pmol/L). MRI interpretation is performed by two independent neuroradiologists (one from the recruiting center and one from the pilot center). In case of discrepancies, a third independent interpretation will be performed by a neuroradiologist from the coordinating center. Abnormal pituitary MRI (thickened pituitary stalk pituitary tumor, ectopic neurohypophysis, septo-optic dysplasia, empty sellar, Rathke pouch) allows a diagnosis of CDI leading to etiological investigations and AVP treatment."

Patients with basal copeptin ≥ 3.53 pmol/l (PP group), and UD patients with normal MRI have gradual reduction of water intake at home without AVP treatment : gradual reduction with 20% in the first week, 30% in the second, 40% in the third, reaching 50% of daily fluid in the last week including restriction overnight, deletion drink before sleep. Some recommendations will be provided to help physicians. For all these latest patients, a clinical reassessment (weight, height, heart rate, blood pressure, input/output 24 hours balance) is performed one month later.