Thyroid Dysfunction and Renal Function: A Crucial Relationship to Recognize

Background and Aim: Renal function is noticeably altered in both hypothyroidism and hyperthyroidism. However, clinical studies on thyroid dysfunction and its association with renal function are scarce. The purpose of this study was to evaluate changes in biochemical parameters of renal function in subjects with thyroid dysfunction and to correlate these values with the patient's thyroid profile. The effect of changes in thyroid function during therapy on renal function was also investigated. Methods: A prospective cohort study included 41 patients with untreated primary hypothyroidism and 16 patients with untreated hyperthyroidism. Thyroid-stimulating hormone (TSH), free thyroxine, and free triiodothyronine were assessed using immunoassay. The estimated glomerular filtration rate was calculated by the Modification of Diet in Renal Disease formula. Renal function tests were assessed in all patients at each of the two-time points: during thyroid dysfunction (hypo- or hyperthyroidism) and after attaining euthyroidism. Results: Our study demonstrated a statistically significant reduction in the average serum creatinine level in the hypothyroid patients after treatment compared to before treatment whereas the mean estimated glomerular filtration rate (eGFR) significantly improved after treatment compared to before treatment. Moreover, the average serum creatinine level in the hyperthyroid patients was significantly lower before treatment compared to after treatment, whereas the mean eGFR significantly dropped after treatment. TSH had a significant positive correlation with serum creatinine and a significant negative correlation with eGFR in all patients with thyroid dysfunction. Conclusions: Thyroid dysfunction is associated with deranged kidney function. It is crucial for the clinician to be aware of the link between thyroid disorders and aberrant renal function in order to consider a thyroid function test when treating a patient whose biochemical markers of renal function are only mildly elevated. There is a need for monitoring creatinine in patients with thyroid dysfunction.