Hypothyroidism as a Cause of Hyponatremia: Fact or Fiction?

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Hypothyroidism as a Cause of Hyponatremia: Fact or Fiction?

Endocr Pract. 2012 Sep 14;:1-11

Authors: Sun G, Pantalone KM, Hatipoglu B


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 (EHR) to identify 10 patients with primary hypothyroidism and same-day serum TSH, sodium, creatinine and calculated glomerular filtration rate (GFR). Same-day free triiodothyronine (FT3) or free thyroxine (FT4) was also recorded if tested. Patients were included in our case series if they met the following inclusion criteria: TSH level >100 ?U/mL and same-day sodium and creatinine levels. All lab tests were collected on an outpatient basis.Results: The 10 subjects (2 men/8 women) were ages 19-97 years (median 51 years). Median TSH was 193 ?U/mL (range 104.2-515.6; normal 0.40-5.50) with median sodium of 138 mmol/L (range 136-142; normal 135-146). The lowest sodium was 136 mmol/L with concurrent TSH of 469.7 ?U/mL, FT3 of 1.0 pg/mL (normal 1.8-4.6) and FT4 of 0.2 ng/dL (normal 0.7-1.8). Median GFR was 67.5 mL/min/1.73m2 (range 44-114; normal 90-120).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.Abbreviations: EHR, electronic health record; FT3, free triiodothyronine; FT4, free thyroxine; GFR, glomerular filtration rate; LT4, levothyroxine; SD, standard deviation; TSH, thyroid stimulating hormone.

PMID: 22982798 [PubMed - as supplied by publisher]

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