Endocrine Abstracts

Background: Several case reports and a few studies reported that hypothyroid patients have elevated serum potassium (K+) levels. However, hypothyroidism has not been widely accepted as a cause of hyperkalemia. This study aims to determine the incidence of hyperkalemia and factors influencing serum K+ levels in thyroid cancer patients who have hypothyroidism due to thyroid hormone withdrawal before radioactive iodine (RAI) treatment.

Methods: We retrospectively reviewed the electronic medical records of 956 patients with thyroid cancer and post-thyroidectomy who underwent RAI in Ramathibodi hospital between January 2017 and June 2021. Demographic data, medication history, and laboratory parameters including serum K+ level and thyroid function tests in patients were collected in both euthyroid (<1 year prior to RAI) and hypothyroid states. The incidence of hyperkalemia and factors influencing serum K+ levels were evaluated.

Results: A total of 508 patients (mean age 52 years, female 79.3%) were included in the final analysis. The incidence of hyperkalemia (K+ ≥5.0 mEq/l) was 2.76%. No patients had developed severe hyperkalemia (K+ ≥6.5 mEq/l). The mean of serum K+ level in the hypothyroid state was significantly higher than in the euthyroid state (4.18±0.38 mEq/l vs 4.13±0.36 mEq/l, P < 0.01). The mean of change in serum K+ level between euthyroid and hypothyroid state was 0.05±0.39 mEq/l. Several factors were associated with serum K+ level in the hypothyroid state (positive correlation: age, use of angiotensin-converting enzyme inhibitors/angiotensin-II receptor blockers, metformin, serum creatinine, serum K+ level during the euthyroid state; and negative correlation: use of thiazide). During the hypothyroid state, hyperkalemia had more developed in patients with serum K+ higher than 4.2 mEq/l (OR 8.83, P < 0.01) or serum FT4 higher than 1.38 ng/dL (OR 7.05, P < 0.01) in the euthyroid state.

Conclusion: The incidence of hyperkalemia was low in hypothyroid patients in our cohorts. However, physicians should raise awareness of hyperkalemia in patients who have baseline serum K+ = 4.2 mEq/l or serum FT4 ≥1.38 ng/dL.