Exploring Thyroid Function after Kidney Transplantation: The Complex Interplay Unacknowledged in Post-Transplant Care

Background/Objectives: The interplay between thyroid function and kidney graft function following kidney transplantation remains incompletely understood. Thyroid disorders are more prevalent in kidney transplant recipients than in the general population and are associated with poorer outcomes. Methods: This prospective, single-center study was designed to estimate thyroid function (thyroid-stimulating hormone (TSH), triiodothyronine (T3), free triiodothyronine (FT3), thyroxine (T4), free thyroxine (FT4), as well as anti-thyroid peroxidase antibody (anti-TPO), anti-thyroglobulin antibody (anti-Tg), and thyroid-stimulating immunoglobulin (TSI)) and its influence on kidney graft function among a cohort of 23 kidney transplant recipients during a follow-up period of 12 months. Results: Significantly increased levels of T4 and T3 were observed 12 months post-transplantation, with FT3 levels increasing significantly after 6 months. The prevalence of immeasurably low anti-Tg antibodies rose during follow-up. Initially, 8% of patients showed positive TSI, which turned negative for all after 6 months. A statistically significant correlation was found between the initial TSH and the estimated glomerular filtration rate (eGFR) value 6 months after transplantation (p = 0.023). The graft function was stable. Proteinuria was statistically significantly lower 12 months after transplantation. Conclusions: Identifying additional risk factors, understanding their impact on kidney graft function, and recognizing cardiovascular comorbidities could enhance patient care. Notably, this study marks the first prospective investigation into thyroid function after kidney transplantation in Croatia, contributing valuable insights to the global understanding of this complex interplay.