Is there a correlation between hypothyroidism and hypokalemia?

Hypothyroidism and Hypokalemia: No Direct Correlation

There is no established correlation between hypothyroidism and hypokalemia; in fact, hypothyroidism is associated with hyperkalemia (elevated potassium), not hypokalemia (low potassium).

The Actual Relationship: Hypothyroidism Causes Hyperkalemia

The evidence consistently demonstrates that hypothyroidism leads to elevated serum potassium levels through specific physiological mechanisms:

• Acute hypothyroidism significantly increases serum potassium levels, as demonstrated in thyroid cancer patients undergoing levothyroxine withdrawal, where mean potassium rose from 4.09 to 4.23 mEq/L (P<.001) 1
• The mechanism involves decreased glomerular filtration rate (eGFR) and reduced plasma renin activity (PRA), both of which impair potassium excretion in the hypothyroid state 2
• Hyperkalemia occurred in 2.8-4.6% of hypothyroid patients in recent studies, while hypokalemia was rare (1.9%) and likely due to other causes 1, 3

Why Hyperthyroidism (Not Hypothyroidism) Causes Hypokalemia

The confusion may arise from the opposite thyroid condition:

• Hyperthyroidism (excess thyroid hormone) causes hypokalemia through increased Na+K+ATPase pump activity, which shifts potassium intracellularly 4
• Thyrotoxic hypokalemic periodic paralysis is a well-recognized complication of hyperthyroidism presenting with profound hypokalemia and muscle weakness 4

Clinical Risk Factors for Hyperkalemia in Hypothyroidism

When hypothyroidism does elevate potassium, certain factors increase risk:

• Age >60 years increases odds of significant hyperkalemia (OR 4.66, P=.026) in hypothyroid patients 1
• Use of RAAS inhibitors (ACE inhibitors or ARBs) increases risk (OR 3.53-9.36) as these medications independently raise potassium 1, 3
• Baseline potassium ≥4.2 mEq/L in the euthyroid state predicts hyperkalemia development (OR 9.36, P<.01) 3
• Diabetes mellitus and reduced eGFR correlate with higher potassium levels in hypothyroid states 3

Important Clinical Pitfalls

• Do not attribute hypokalemia to hypothyroidism—if a hypothyroid patient presents with low potassium, search for alternative causes such as diuretic use, gastrointestinal losses, or inadequate intake 5
• Monitor potassium in elderly hypothyroid patients on RAAS inhibitors, as this combination poses the highest risk for clinically significant hyperkalemia 1, 3
• The hyperkalemia from hypothyroidism is typically mild and asymptomatic, with severe hyperkalemia (≥6.5 mEq/L) not reported in recent cohorts 3

Monitoring Recommendations

• Check serum electrolytes including potassium when diagnosing or treating thyroid dysfunction, particularly in patients with risk factors 5
• Serial potassium monitoring is warranted in hypothyroid patients over 60 years old, those with renal impairment, or those taking medications affecting potassium homeostasis 1, 3