The relationship between thyroid function and estimated glomerular filtration rate in patients with chronic kidney disease

Background. Recent studies have shown an increasing risk of hypothyroidism with incrementally lower estimated glomerular filtration rate (eGFR) in cohorts comprised of patients with normal to mildly impaired kidney function. We sought to confirm these findings in a nationally representative cohort of Veterans Affairs patients with moderate-to-severe chronic kidney disease (CKD). Methods. This study examined the association between kidney function and hypothyroidism among 461 607 veterans with Stage 3 to 5 CKD who underwent repeated measurements of serum creatinine and thyrotropin (TSH) at identical time points between October 2004 and September 2006. Kidney function was defined by eGFR using the Chronic Kidney Disease Epidemiology Collaboration formula. In primary analyses, the association between eGFR and hypothyroidism (defined as serum TSH > 5 mIU/L and/or receipt of thyroid hormone supplementation) was estimated using multivariable random effects logistic regression. In secondary analyses, the association between eGFR and serum TSH level was estimated using multivariable random effects linear regression. Results. At baseline, 68.9, 25.5, 5.3 and 0.3% of patients had Stage 3A, 3B, 4 and 5 CKD, respectively. For every 10 mL/min/1.73 m(2) lower eGFR, there was an 18% higher risk of hypothyroidism: adjusted odds ratio 1.18 [95% confidence interval (CI) 1.17-1.20, P < 0.001]. In secondary analyses, we observed that a 10 mL/min/1.73 m(2) lower eGFR was associated with a 0.11 mIU/L higher serum TSH (95% CI 0.10-0.11 mIU/L higher serum TSH, P < 0.001). Conclusions. In a nationally representative cohort of patients with moderate-to-severe CKD, there is an inverse association between eGFR and risk of hypothyroidism.