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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.

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).

CONCLUSION:

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.

PMID:
22982798
[PubMed - indexed for MEDLINE]
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