Association of thyroid functional disease with mortality in a national cohort of incident hemodialysis patients

Context: Hypothyroidism is a common condition that disproportionately affects hemodialysis patients. In the general population, hypothyroidism is associated with higher mortality, particularly in populations with underlying cardiovascular risk. Despite their heightened cardiovascular mortality, the impact of hypothyroidism on the survival of hemodialysis patients remains uncertain. Objective: To examine whether hypothyroidism is independently associated with higher mortality in hemodialysis patients. Design, Setting, and Patients: Among 8840 incident hemodialysis patients receiving care from a large national dialysis provider from January 2007 to December 2011, weexamined the association of hypothyroidism (TSH >5.0 mIU/L) with mortality. Main Outcome Measures: Associations between baseline and time-dependent hypothyroidism with all-cause mortality were determined using case-mix adjusted Cox models. In secondary analyses, weexamined the impact of low-normal, upper-normal, subclinical range, and overt range TSH levels (TSH ≥0.5-3.0, >3.0-5.0, >5.0-10.0, and >10.0 mIU/L, respectively) on mortality risk. Results: The study population consisted of 1928 (22%) hypothyroid and 6912 (78%) euthyroid patients. Baseline and time-dependent hypothyroidism were associated with higher mortality: adjusted hazard ratios (95% confidence intervals) were 1.47 (1.34-1.61) and 1.62 (1.45-1.80), respectively. Compared to low-normal TSH, upper-normal, subclinical hypothyroid, and overt hypothyroid TSH levels were associated with incrementally higher adjusted death risk in baseline and time-dependent analyses. In time-dependent analyses, the hypothyroidism-mortality association was increasingly stronger across higher body mass index strata. Conclusions: Hypothyroidism as well as upper-normal TSH levels are associated with higher mortality in hemodialysis patients. Further studies are needed to determine whether restoration of TSH to low-normal levels with thyroid hormone replacement therapy ameliorates adverse outcomes in hemodialysis patients.