The background of the study. Water-soluble radiographic contrast agents contain large amounts of iodide, which can lead to changes in thyroid function weeks later. This study evaluated the acute effects of these agents on thyroid function in normal subjects.
How the study was done. The study subjects were 22 patients who underwent elective coronary arteriography or computed tomography, during which they received intravenous injections of a water-soluble radiographic contrast agent. None had a history of thyroid disease or was seriously ill, and all had normal serum thyrotropin (TSH) and free thyroxine (T4) concentrations. These hormones were measured twice before and daily for seven days after contrast administration.
The results of the study. The total doses of iodide administered were very high, ranging from 300 to 1121 mg/kg of body weight. The patients’ serum free T4 concentrations did not change, but their serum TSH concentrations increased slightly but statistically significantly on days 3 and 4 (Table).
|Table. Average Serum Free T4 and TSH Concentrations in 22 Patients before and after Radiographic Contrast Agent Administration.|
|Free T4 (ng/dl)||1.34||1.28||1.33||1.28||1.29||1.25||1.23||1.40|
The mean maximal increase in serum TSH was 2.4 mU/L, and four patients had values slightly above the normal range at some time.
The conclusions of the study. In patients with normal thyroid function, intravenous administration of a radiographic contrast agent has little effect on serum T4 concentrations, but may cause a small transient increase in TSH secretion.
The original article. Gartner W, Weissel M. Do iodine-containing contrast media induce clinically relevant changes in thyroid function parameters of euthyroid patients within the first week? Thyroid 2004;14:521-4.