[The 20 min. iodine uptake in Graves' disease. 1. Technique and reliability (author's transl)]

The 20 minute intravenous radioiodine uptake technique is described in detail and results compared with those from the classical 2 1/2 hour oral uptake in 93 Graves' disease patients. Two methods used in correcting for extrathyroidal radioactivity in the early uptake are similarly compared. The 20 minute uptake was normal (locally less than 8% dose) in only 6,5% of the patients while the 2 1/2 hour uptake was normal (locally less than 35% dose) in 18,5%; in six patients the uptake at 20 min. was higher than at 2 1/2 h, observations indicating the superior sensitivity and diagnostic value of the early uptake. The suppression test performed at 20 minutes was, furthermore, pathological in 97,8% of patients. The comparison of methods to correct for extrathyroidal radioactivity in the 20-minute test showed excellent agreement between thigh count subtraction and application of a formula based on the thyroid uptake at 2 minutes. The former technique, however, was considered to be simpler. We conclude that the 20 minute intravenous iodine uptake technique is not only simpler to perform than the classical oral method, but is also diagnostically more accurate. A high quality scan was obtained 30-60 minutes after the injection of radioiodine in most of these patients.