The effect of iodine containing contrast medium on thyroid function of patients undergoing coronary angiography

Application of large amounts of iodine in the form of amidotricoic acid (Urografin) in 20 patients undergoing coronary angiography led to an increase in serum thyroxine (T4, p less than 0.005), triiodothyronine (T3, p less than 0.005) and plasma thyrotropin (TSH) in the basal state (p less than 0.05) as well as after TRH-stimulation (p less than 0.05), but not of serum 3,3',5'-triiodothyronine (reverse-T3, rT3) three weeks after contrast medium administration. Although TRH induced TSH stimulation had been subnormal prior to contrast medium application in five patients, T4 as well as T3 remained within the normal range in all patients. Neither preexisting iodine excretion nor the amount of contrast medium applied were related with the observed hormonal changes. We conclude, that application of relatively small as well as large amounts of amidotricoic acid leads to an increase of peripheral thyroid hormone concentrations, paralleled by a rise in basal and stimulated TSH secretion. These changes may be interpreted as physiological adaptation to augmented iodine supply in an area of moderate iodine deficiency.