Hyperkalemia develops in some thyroidectomized patients undergoing thyroid hormone withdrawal in preparation for...

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.

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).

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.

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 reninangiotensin-aldosterone system.