Objective: To determine whether increases in BUN and serum creatinine (SCr) concentrations, which have been reported to develop after surgical bilateral thyroidectomy in hyperthyroid cats, also develop after treatment of hyperthyroidism with radioactive iodine and methimazole.
Design: Prospective, clinical trial.
Animals: 58 hyperthyroid cats.
Procedure: Urine specific gravity, SCr, BUN, and serum thyroxine (T4) concentrations were determined before and 30 and 90 days after treatment of hyperthyroidism with radioactive iodine, methimazole, or surgical bilateral thyroidectomy.
Results: Mean SCr and BUN concentrations determined 30 and 90 days after treatment were significantly higher than those measured before treatment. Mean SCr, BUN, and T4 concentrations were not different among groups before treatment or 30 and 90 days after treatment.
Clinical implications: Reduction of serum T4 concentrations after treatment of hyperthyroidism may result in azotemia in older cats with chronic renal disease. Treating azotemic hyperthyroid cats with methimazole until it can be determined whether correction of the hyperthyroid state will exacerbate the azotemia may be prudent.