Thyroid status and renal function in older persons in the general population

Background: Prevalence estimates of thyroid dysfunction and chronic kidney disease both increase with age. The aim of this study was to investigate the cross-sectional association between low thyroid function and renal function in subjects aged 85 years and to assess whether a low thyroid function at age 85 years is associated with an accelerated decline in renal function during follow-up. Methods: We included 558 participants from the Leiden 85-plus Study. At baseline (age 85 y), TSH, free T₄ (fT4), and free T₃ levels were measured. Thyroid function groups were created using clinical cutoff values of TSH and fT4. Serum creatinine concentrations were determined at baseline and annually during a 5-year follow-up period. Estimated glomerular filtration rates (eGFRs) were calculated by means of the Modification of Diet in Renal Disease Study equation. Results: At baseline, subjects with higher levels of TSH and lower levels of fT4 and free T₃ had lower renal function. Participants with hypothyroidism [mean 53.7 (2.0) mL/min per 1.73 m2)] and subclinical hypothyroidism [55.7 (2.1) mL/min per 1.73m²] hadlowermeaneGFRs (SE) than participants with normal thyroid function [59.5 (0.7) mL/min per 1.73 m²]; the highest eGFR was observed in participants with hyperthyroidism [eGFR 61.5 (3.1) mL/min per 1.73m²] (P for trend = .004). There was no association between thyroid hormone levels at baseline and the change in renal function during follow-up. Conclusions: Although low thyroid function was associated with lower renal function at age 85 years, an association between a low thyroid function and change in renal function over time was absent. Our findings question the causal relevance of the thyroid status for the deterioration of renal function in the oldest old.