HYPERKALEMIA DEVELOPS IN SOME THYROIDECTOMIZED PATIENTS UNDERGOING THYROID HORMONE WITHDRAWAL IN PREPARATION FOR RADIOACTIVE IODINE ABLATION FOR THYROID CARCINOMA

Objective: Hyponatremia is observed in hypothyroidism, but it is not known if hypo-or hyperkalemia is associated with hypothyroidism. To study these questions, we determined serum potassium (K+) levels in thyroidectomized patients undergoing levothyroxine withdrawal before radioactive iodine (RAI) therapy for thyroid carcinoma. Methods: We retrospectively studied the records of 108 patients who had undergone total thyroidectomy for thyroid carcinoma followed by levothyroxine withdrawal and then ablation with RAI at Nagasaki University Hospital from 2009-2013. Blood samples were analyzed for serum K+ concentrations when patients were euthyroid just before levothyroxine withdrawal and hypothyroid 21 days after levothyroxine withdrawal. We determined the proportion of patients who developed hyperkalemia (K+ >= 5 mEq/L) and hypokalemia (K+ <= 3.5 mEq/L). Results: Five (4.6%) patients developed hyperkalemia and 2 (1.9%) patients developed hypokalemia after levothyroxine withdrawal. The mean serum K+ level after levothyroxine withdrawal was significantly higher than before levothyroxine withdrawal (4.23 +/- 0.50 mEq/L vs. 4.09 +/- 0.34 mEq/L; P<.001). After levothyroxine withdrawal, serum K+ values were significantly correlated with age, serum sodium and creatinine levels, and the estimated glomerular filtration rate but not with serum free thyroxine or thyroid-stimulating hormone concentrations. The finding of an elevated serum K+ of > 0.5 mEq/L after levothyroxine withdrawal was more prevalent with age > 60 years (odds ratio [OR], 4.66; P = .026) and with the use of angiotensin-II receptor blockers or angiotensin-converting enzyme inhibitors (OR, 3.53; P = .033) in a multivariate analysis. Conclusion: Hyperkalemia develops in a small percentage of hypothyroid patients after thyroid hormone withdrawal, especially in patients over 60 years of age who are using antihypertensive agents that inhibit the renin-angiotensin-aldosterone system.