title: Hyponatremia and mortality risk: a Danish cohort study of 279 508 acutely hospitalized patients.
abstract: OBJECTIVE
  We aimed to investigate the impact of hyponatremia severity on mortality risk and assess any evidence of a dose-response relation, utilizing prospectively collected data from population-based registries.
  
  
  METHODS
  Cohort study of 279 ,508 first-time acute admissions to Departments of Internal Medicine in the North and Central Denmark Regions from 2006 to 2011.
  
  
  METHODS
  We used the Kaplan-Meier method (1 - survival function) to compute 30-day and 1-year mortality in patients with normonatremia and categories of increasing hyponatremia severity. Relative risks (RRs) with 95% CIs, adjusted for age, gender and previous morbidities, and stratified by clinical subgroups were estimated by the pseudo-value approach. The probability of death was estimated treating serum sodium as a continuous variable.
  
  
  RESULTS
  The prevalence of admission hyponatremia was 15% (41,803 patients). Thirty-day mortality was 3.6% in normonatremic patients compared to 7.3, 10.0, 10.4 and 9.6% in patients with serum sodium levels of 130-134.9, 125-129.9, 120-124.9 and <120 mmol/l, resulting in adjusted RRs of 1.4 (95% CI: 1.3-1.4), 1.7 (95% CI: 1.6-1.8), 1.7 (95% CI: 1.4-1.9) and 1.3 (95% CI: 1.1-1.5) respectively. Mortality risk was increased across virtually all clinical subgroups, and remained increased by 30-40% 1 year after admission. The probability of death increased when serum sodium decreased from 139 to 132  mmol/l. No clear increase in mortality was observed for lower concentrations.
  
  
  CONCLUSIONS
  Hyponatremia is highly prevalent among patients admitted to Departments of Internal Medicine and is associated with increased 30-day and 1-year mortality risk, regardless of underlying disease. This risk seems independent of hyponatremia severity.
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark louise.bill@clin.au.dk.
authors.forename: Louise
authors.initials: L
authors.lastname: Holland-Bill
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Christian Fynbo
authors.initials: CF
authors.lastname: Christiansen
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Uffe
authors.initials: U
authors.lastname: Heide-Jørgensen
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Sinna Pilgaard
authors.initials: SP
authors.lastname: Ulrichsen
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Troels
authors.initials: T
authors.lastname: Ring
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Jens Otto L
authors.initials: JO
authors.lastname: Jørgensen
authors.affiliation: Department of Clinical EpidemiologyAarhus University Hospital, Olof Palmes Allé 43-45, DK-8200 Aarhus N, DenmarkDepartment of NephrologyAalborg University Hospital, Aalborg, DenmarkDepartment of Endocrinology and Internal MedicineAarhus University Hospital, Aarhus C, Denmark.
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015897:Comorbidity; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006760:Hospitalization; D006801:Humans; D007010:Hyponatremia / Q000401:mortality*; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries; D018570:Risk Assessment; D012737:Sex Factors; D012964:Sodium / Q000097:blood; D055815:Young Adult
chemical_list: D012964:Sodium