Retention of iodine after tracer doses in patients with iodine accumulating thyroid cancer

In patients with iodine-accumulating thyroid cancer whole body iodine retention after tracer doses of 131-iodine (20 μCi - 740 kBq) is a sensitive method to detect accumulating secondaries. It is easy to perform and devoid of any major radiation hazards for both the patients and the staff. Successful screening application require stringent criteria for patient selection (condition after total thyroidectomy and condition after destruction of residual thyroid tissue with at least 80 mCi (3 GBq) 131-iodine). Under these conditions whole body iodine retention showed a sensitivity of 0.72 and a specificity of 0.93 for detecting iodine-accumulating secondaries in the 249 patients with accumulating thyroid cancer examined sofar. For serum thyreoglobulin sensitivity and specificity were found to be 0.89 and 0.96. The combination of these two tests gave a sensitivity of 0.95 and a specificity of 0.96. Post-treatment whole body scans served as reference. The high sensitivity and specificity and the uselessness of serum thyreoglobulin levels in the presence of thyroid antibodies (11% of our patients) suggest whole body iodine retention to offer substantial advantages in the detection of iodine-accumulating secondaries. (Author)