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Endocr Pract. 2012 Nov-Dec;18(6):894-7. doi: 10.4158/EP12130.OR.

Hypothyroidism as a cause of hyponatremia: fact or fiction?

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  • 1Endocrinology and Metabolism Section, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.



To illustrate that severe primary hypothyroidism alone may not be enough to cause hyponatremia in the otherwise healthy ambulatory patient.


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.


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).


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.

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