Accuracy Considerations When Using Early (Four- or Six-Hour) Radioactive Iodine Uptake to Predict Twenty-Four-Hour Values for Radioactive Iodine Dosage in the Treatment of Graves' Disease

Abstract

Although literature has offered methods to predict 24-hour radioactive iodine uptake values from early (4- to 6-hour) measurements, the resultant dosage errors have not been examined. Potential errors include underdosage, overdosage, and a failure to recognize rapid turnover patients (early-to-late uptake ratios > or = 1) who are at high risk for treatment failure and full-body radiation exposure. We developed and tested a novel method for minimizing error involved in using a single early uptake measurement to derive late uptake. From a retrospective analysis of 203 Graves' disease patients, receiver operating characteristic (ROC) curve analysis enabled us to identify patients likely to experience rapid turnover and therefore should receive 24-hour studies. Twenty-four-hour uptake measurements are necessary with 77% or more 4-hour uptake values and 80% or more 6-hour values. After eliminating these patients, we developed linear regression equations to predict the 24-hour uptake from 4-hour (n = 61) and 6-hour (n = 22) rule groups, testing their efficacy on separate 4-hour (n = 61) and 6-hour (n = 21) patient groups. We also used our test population to measure error in four early-to-late uptake conversion formulas presented in the literature. Error involved in these predictions ranged from a 10.6% overestimate for 4-hour calculations to a 5.9% underestimate for 6-hour calculations. When applied to two dosage formulas incorporating gland size, absorbed dose, and 24-hour uptake, average dosage error was 7%. In comparison to the other sources of error radioactive iodine (131I) dosimetry, potential error in predicting 24-hour uptake from 4- or 6-hour uptake values is low.

Prediction of late (24-hour) radioactive iodine uptake using early (3-hour) uptake values in Japanese patients with Graves’ disease

“…All other factors, including gender (P = 0.266), age (P = 0.452), thyroid volume (P = 0.291), TSH (P = 0.497), FT4 (P = 0.096), Cre (P = 0.282), TRAb2 (P discussion Table 3 compares the present early-to-late RAIU conversion equation and several other early-to-late RAIU conversion equations that have been previously reported by other investigators [1,3,4]. These previously reported equations suggest a stronger correlation between early RAIU and late RAIU than the present equation, which employs only 3-hour RAIU.…”

“…In the present study, none of the patients with Graves' disease had rapid turnover. Morris et al [4] also reported that Graves' disease patients with 4-hour RAIU values of 77% or greater also should obtain 24-hour RAIU values, probably due to rapid turnover. However, only 7 of 66 patients had 3-hour RAIU values greater than 77% in the present study, and none of those 7 patients had rapid turnover.…”

“…Several other investigators have reported that patients with hyperthyroidism or Graves' disease have "rapid turnover" (24-hour RAIU value is less than the 3-to 4-hour RAIU value; typically characterized by a significantly increased early RAIU value) [3,4,10,11]. Furthermore, Marcocci et al [10] and Atkay et al [11] reported that rapid turnover is a statistically significant predictor of RI therapy failure because of rapid clearance or turnover of RI from the thyroid gland.…”

“…RI therapy failure rates were reported to be 55% in 87 Graves' disease patients and 48% in 67 hyperthyroidism patients with rapid turnover, compared to 21% in 187 Graves' disease patients and 11% in 366 hyperthyroidism patients without rapid turnover [10,11]. The prevalence of rapid turnover was reported to be 32% in 274 patients with Graves' disease by Marcocci et al [10], 15% in 433 patients with hyperthyroidism (including 379 patients with Graves' disease) by Atkay et al [11], 17% in 69 patients with Graves' disease by Vemulakonda et al [3], and 12% in 148 patients with Graves' disease by Morris et al [4]. In the present study, none of the patients with Graves' disease had rapid turnover.…”

Differentiation between Graves' disease and painless thyroiditis by diffusion-weighted imaging, thyroid iodine uptake, thyroid scintigraphy and serum parameters

“…Although RAIU is the most reliable method to differentiate GD from PT (11)(12)(13)(14), it is contraindicated when patients are lactating, and not all clinics are well equipped to perform RAIU. Therefore, a number of studies have been undertaken to search for simple and practical parameters that might allow differentiation between the two entities.…”