Thyroid Function With Continuous Kidney Replacement Therapy: A Prospective Study

Background: Acute kidney injury (AKI) and end stage kidney disease (ESKD) requiring continuous kidney replacement therapy (CKRT) are associated with high mortality. Solutes up to 40 kilodaltons (kDa) in size are amenable to CKRT clearance which includes thyroid stimulating hormone (TSH)(28 kDa), free thyroxine (fT4)(0.78 kDa), and free triiodothyronine (fT3)(0.68 kDa). The effect of CKRT on TSH and thyroid hormone clearance, thyroid function, and the hypothalamic-pituitary-thyroid (HPT) axis is unknown. Methods: This prospective, single-center observational study enrolled 50 ICU patients requiring CKRT and 50 control ICU patients. Serum TSH, fT4, fT3, and reverse T3 (rT3) were measured prior to and on days 1, 3, 8, and 14 after CKRT initiation; effluent TSH, fT4, and fT3 were measured on days 1, 3, 8, and 14. Thyroid function status was adjudicated on days 1, 3, 8, and 14. Statistical analyses included Fisher’s exact tests, unpaired t-tests, and Fisher’s Least Significant Difference tests to compare differences in thyroid hormones and Sequential Organ Failure Assessment (SOFA) scores. Results: Prior to and during CKRT, CKRT patients had reduced TSH, fT4, and fT3 levels compared to controls, with a higher proportion of values below the normal reference range. TSH and fT4 were present in the CKRT effluent, indicating clearance by CKRT. More severe and prolonged non-thyroidal illness syndrome (NTIS) was seen in the CKRT cohort compared to controls with similar severity of illness as judged by SOFA scores. No CKRT patient achieved euthyroid status during the study. Conclusions: This is the first study to assess thyroid function in CKRT patients. We demonstrate that patients requiring CKRT have a greater rate, severity, and duration of NTIS versus ICU controls, which may be affected by removal of TSH and fT4. These novel complications may contribute to the high mortality rate observed in patients with either AKI or ESKD who require CKRT. Trial Registration Not applicable