Pre- and Post-Radioactive Iodine Therapy Hormonal Changes and Clinical Outcomes in Hyperthyroid Patients: A Retrospective Cohort Study.

Objective: To assess changes in thyroid hormone levels following radioactive iodine (RAI) therapy, evaluate post-treatment clinical outcomes, and identify factors associated with thyroid status among hyperthyroid patients treated at a tertiary care hospital in Peshawar. Methodology: This was a retrospective cohort study conducted at Nuclear Medicine and Endocrinology Department of Northwest General Hospital, from January 2022 to December 2024. A total of 83 adult patients with Graves' disease, toxic adenoma, or toxic multinodular goiter who received RAI therapy were included. RAI was administered using a fixed-dose protocol based on clinical diagnosis and disease severity. Antithyroid drugs were discontinued prior to RAI as per standard institutional protocol. Baseline demographic and clinical characteristics, including age, gender, and diagnosis, were recorded. Thyroid hormone levels (Free T4, T3, and TSH) were measured at baseline and six months post-treatment. Data on thyroid gland size and TRAb levels were not routinely available and therefore not included in the analysis. Only patients with complete six-month follow-up data were analyzed. Pre- and post-treatment hormone levels were compared using the Wilcoxon Signed-Rank Test, and binomial logistic regression was used to identify predictors of thyroid status. Results: The mean age of patients was 49.76±15.2 years, predominantly female (69%). Graves' disease was the most common diagnosis (54.8%). At six months post-RAI therapy, 44.0% developed hypothyroidism, 41.7% became euthyroid, and 14.3% remained hyperthyroid. Post-treatment thyroid status was significantly associated with underlying diagnosis (p < 0.001), while no significant associations were observed with age (p=0.060) or gender (p = 0.364). Significant reductions in Free T4 (2.19 to 1.01 ng/dl) and T3 (2.01 to 1.02 ng/dl), along with an increase in TSH (0.01 to 3.65 mIU/L), were observed following RAI therapy (p<0.001). On regression analysis, Graves' disease was identified as a significant predictor of post-treatment hypothyroidism (adjusted OR=16.48, 95% CI: 3.14-86.58; p=0.001), whereas age, gender, toxic adenoma, and RAI dose were not statistically significant predictors. Conclusion: RAI therapy was associated with hypothyroidism as a common outcome, particularly among patients with Graves' disease, while other clinical factors showed limited association with post-treatment thyroid status.