Quantitative analysis of the relation between urinary iodine concentration and thyroid iodine uptake rate in newly diagnosed Graves’ disease: a single-center retrospective study

The efficacy of radioactive iodine-131 (RAI) therapy for Graves' disease (GD) depends on thyroid iodine uptake, which may be influenced by iodine status. This study investigated the relationship between urinary iodine concentration (UIC) and RAI uptake (RAIU) in newly diagnosed, drug-naive GD patients. We retrospectively analyzed 248 patients with GD who underwent RAIU measurements at 2, 4, and 24 h after iodine-131 administration. UIC was measured using arsenic-cerium catalytic spectrophotometry. RAIU was calculated using standardized counts, and correlations with UIC were assessed via Pearson's correlation and linear regression. Group comparisons were performed with analysis of variance or Mann-Whitney U tests. The median UIC was 222.52 μg/L. Female patients had higher RAIU than males at all time points. RAIU declined with age (P < 0.05). Elevated UIC showed significant inverse correlations with RAIU-2 h (r = -0.15, P = 0.015), RAIU-4 h (r = -0.21, P = 0.001), and RAIU-24 h (r = -0.28, P < 0.001). Notably, patients with UIC > 300 μg/L demonstrated a 15-20% reduction in RAIU compared with those with normal UIC (100-300 μg/L). Gender, age, and some renal function indices showed no significant correlation with UIC. This retrospective study adds some quantitative evidence on the relationship between UIC and RAIU in patients with newly diagnosed GD, further demonstrating that higher UIC values are associated with suppressed RAIU. These findings highlight the importance of pre-therapeutic UIC screening to optimize RAI dosing and planning, particularly in regions with variable dietary iodine intake.