title: The water deprivation test and a potential role for the arginine vasopressin precursor copeptin to differentiate diabetes insipidus from primary polydipsia.
abstract: The water deprivation test is the gold standard test to differentiate central or nephrogenic diabetes insipidus (DI) from primary polydipsia (PP) in patients with polyuria and polydipsia. Few studies have addressed the diagnostic performance of this test. The aim of this retrospective cohort study was to evaluate the diagnostic performance of the standard water deprivation test, including plasma arginine vasopressin (AVP) measurements, in 40 consecutive patients with polyuria. We compared initial test results with the final clinical diagnosis, i.e., no DI, central DI, or nephrogenic DI. The median length of follow-up was 8 years. In a subset of ten patients, the novel marker copeptin (CP) was measured in plasma. Using the final diagnosis as a gold standard, a threshold for urine osmolality of >800 mOsmol/kg after water deprivation yielded a sensitivity and specificity of 96 and 100%, respectively, for diagnosing PP. Sensitivity increased to 100% if the cut-off value for urine osmolality was set at 680 mOsmol/kg. Plasma AVP levels did not differ between patient groups and did not differentiate among central DI, nephrogenic DI, or PP. In all three patients with central DI, plasma CP was <2.5 pmol/l with plasma osmolality >290 mOsmol/kg, and >2.5 pmol/l in patients without DI. The optimal cut-off value for differentiating PP from DI during a water deprivation test was urine osmolality >680 mOsmol/kg. Differentiating between central and nephrogenic DI should be based on clinical judgment as AVP levels did not discriminate.
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands m.defost@amc.uva.nl.
authors.forename: M
authors.initials: M
authors.lastname: de Fost
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: S M
authors.initials: SM
authors.lastname: Oussaada
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Endert
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: G E
authors.initials: GE
authors.lastname: Linthorst
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: M J
authors.initials: MJ
authors.lastname: Serlie
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: M R
authors.initials: MR
authors.lastname: Soeters
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: DeVries
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: P H
authors.initials: PH
authors.lastname: Bisschop
authors.affiliation: Department of Endocrinology and MetabolismRoom F5-164Laboratory of EndocrinologyDepartment of Clinical Chemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Fliers
keywords: arginine vasopressin; copeptin; diabetes insipidus; pituitary; polydipsia; polyuria; primary polydipsia; psychogenic polydipsia; water deprivation test