Acute water load test has been using to diagnose renal ability to excrete water for decades. Latest recommendations for the diagnosis of hyponatremia do not recommend performing such a test. The investigators aim at, retrospectively, study the value of acute water load test in patients suffering from a syndrome of inappropriate antidiuresis.

Inclusion Criteria:

• ≥ 18 years old at the time of the test
• affiliated to a social insurance system
• water load test performed at the Renal and Metabolic Diseases Unit of the European George Pompidou Hospital, AP-HP, Paris, France
• between 01/01/2001 and 12/31/2019

Exclusion Criteria:

• hypernatremia and/or polyuria-polydipsia (diabetes insipidus)
• hyponatremia due to a tea and toast syndrome and/or a beer potomania
• hyponatremia due to a high (or normal) osmolality related to diabetes mellitus, hyperproteinemia and/or intoxication
• chronic kidney disease with an estimated glomerular filtration rate (eGFR) by the MDRD formula <60 mL/min/1.73m2
• hyponatremia related to thiazides
• hyponatremia related to an hypovolemic status
• syndrome of inappropriate antidiuresis related to an endocrine disorder (such as hypothyroidism or adrenal insufficiency)

In this retrospective study, the included population is composed only with adult patients experiencing a syndrome of inappropriate antidiuresis (SIAD) who were explored by an acute water load test at the Renal and Metabolic Diseases Unit of the European George Pompidou Hospital, Paris, France.