title: Hypothyroidism as a cause of hyponatremia: fact or fiction?
abstract: OBJECTIVE
  To illustrate that severe primary hypothyroidism alone may not be enough to cause hyponatremia in the otherwise healthy ambulatory patient.
  
  
  METHODS
  A retrospective chart review was conducted using an academic health center enterprise-wide electronic health record to identify 10 patients with primary hypothyroidism and same-day serum thyroid-stimulating hormone (TSH), sodium, creatinine, and calculated glomerular filtration rate (GFR). Same-day free triiodothyronine or free thyroxine was also recorded if tested. Patients were included in our case series if they met the following inclusion criteria: TSH level >100 μU/mL and same-day sodium and creatinine levels. All laboratory tests were collected on an outpatient basis.
  
  
  RESULTS
  The 10 subjects (2 men and 8 women) were ages 19 to 97 years (median, 51.5 years). Median TSH was 193 μU/mL (range, 104.2 to 515.6 μU/mL; normal, 0.40 to 5.50 μU/mL) with median sodium of 138 mmol/L (range, 136 to 142 mmol/L; normal, 135 to 146 mmol/L). The lowest sodium was 136 mmol/L with concurrent TSH of 469.7 μU/mL, free triiodothyronine of 1.0 pg/mL (normal, 1.8 to 4.6 pg/mL), and free thyroxine of 0.2 ng/dL (normal, 0.7 to 1.8 ng/dL). Median GFR was 67.5 mL/min/1.73 m2 (range, 44 to 114 mL/min/1.73 m2; normal, 90 to 120 mL/min/1.73 m2).
  
  
  CONCLUSIONS
  In our small series of patients with extreme TSH elevations, none had a serum sodium level below normal (<135 mmol/L), even in the presence of a reduced GFR. Hyponatremia can be a common occurrence in hospitalized and/or chronically ill patients; however, in an otherwise relatively healthy ambulatory patient, hypothyroidism, even when severely undertreated, may be a less clinically relevant cause of hyponatremia.
authors.affiliation: Endocrinology and Metabolism Section, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.
authors.forename: Grace E Ching
authors.initials: GE
authors.lastname: Sun
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Pantalone
authors.forename: Betul
authors.initials: B
authors.lastname: Hatipoglu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D007010:Hyponatremia / Q000097:blood* / Q000209:etiology*; D007037:Hypothyroidism / Q000097:blood* / Q000150:complications*; D007668:Kidney / Q000502:physiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012964:Sodium / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D012964:Sodium; D003404:Creatinine; D013974:Thyroxine