Does untreated hypothyroidism cause hypernatremia or hypercalcemia?

Hypothyroidism Does Not Cause Hypernatremia or Hypercalcemia

Uncontrolled hypothyroidism causes hyponatremia (low sodium), not hypernatremia, and does not typically elevate calcium levels. The electrolyte disturbances move in the opposite direction from what the question suggests.

Sodium Abnormalities in Hypothyroidism

Hyponatremia, Not Hypernatremia

• Moderate to severe hypothyroidism and myxedema cause hyponatremia (serum sodium <135 mmol/L), not hypernatremia 1
• The mechanism involves decreased free water excretion due to elevated antidiuretic hormone (ADH) levels, primarily attributed to hypothyroidism-induced decreased cardiac output 1
• Hyponatremia in hypothyroidism presents as euvolemic hypo-osmolar hyponatremia with inappropriately elevated urine osmolality 1, 2

Clinical Context and Severity

• Recent evidence suggests that hypothyroidism-induced hyponatremia is relatively rare and probably occurs only in severe hypothyroidism and myxedema, not in mild to moderate cases 1, 3
• When hyponatremia occurs in patients with mild or moderate hypothyroidism, other causes should be actively sought, including medications, infections, or adrenal insufficiency 1, 3
• Severe hyponatremia without myxedema coma should prompt investigation for alternative etiologies rather than attributing it solely to hypothyroidism 3

Critical Diagnostic Pitfall: Rule Out Adrenal Insufficiency

• Adrenal insufficiency must be excluded before diagnosing hypothyroidism as the cause of hyponatremia, as both conditions present with nearly identical laboratory findings 4
• Hyponatremia is present in 90% of newly diagnosed adrenal insufficiency cases and can be indistinguishable from hypothyroidism-related hyponatremia 4, 5
• The standard 0.25 mg cosyntropin stimulation test is medically necessary to rule out adrenal insufficiency in patients with hypo-osmolar hyponatremia 4
• Both hypothyroidism and adrenal insufficiency can cause inappropriate ADH secretion leading to hyponatremia 6

Calcium Abnormalities in Hypothyroidism

No Hypercalcemia in Hypothyroidism

• Hypothyroidism does not cause hypercalcemia (elevated calcium)
• The provided guidelines and research evidence do not support any association between uncontrolled hypothyroidism and elevated calcium levels 7, 1, 2, 8, 3
• Mild hypercalcemia can occasionally occur in adrenal insufficiency (10-20% of cases), but this is unrelated to thyroid function 4

Treatment Approach

Management of Hypothyroidism-Related Hyponatremia

• Thyroid-stimulating hormone (TSH) determination is mandatory during evaluation of patients with reduced serum sodium levels 1
• Treatment with thyroid hormone replacement and fluid restriction are usually adequate for managing mild hyponatremia in hypothyroid patients 1
• Hyponatremia typically resolves with appropriate thyroid hormone substitution therapy 2

When to Suspect Alternative Diagnoses

• If severe hyponatremia occurs without clinical myxedema, actively investigate other potential causes including adrenal insufficiency, SIADH from other etiologies, medications, or infections 1, 3
• Patients with possible hyponatremic encephalopathy require urgent treatment according to current hyponatremia guidelines regardless of thyroid status 1