title: Subclinical hypothyroidism and survival: the effects of heart failure and race.
abstract: BACKGROUND
  Studies examining the association between subclinical hypothyroidism and mortality have yielded conflicting results. Emerging data suggest these associations may depend upon underlying congestive heart failure (CHF) and/or race, but this has not been empirically determined.
  
  
  OBJECTIVE
  Our objective was to examine the association between subclinical hypothyroidism and hypothyroidism overall with mortality according to pre-existing CHF and race.
  
  
  METHODS
  We examined the associations of subclinical hypothyroidism (TSH higher than assay upper limit of normal; total T4 within reference) and hypothyroidism overall (TSH higher than assay upper limit of normal; total T4 below lower limit of normal or within reference) with all-cause mortality among Third National Health and Nutrition Examination Survey participants stratified by CHF and race using multivariable Cox models. To confirm whether differences between strata were statistically significant, we tested for interaction on the basis of CHF (separately) and race by likelihood ratio testing.
  
  
  RESULTS
  There were 14 130 (95.0%) euthyroid controls and 749 (5.0%) participants with hypothyroidism, 691 (4.6%) of whom had subclinical disease. Subclinical hypothyroidism vs euthyroidism was associated with greater mortality in those with CHF but not in those without: adjusted hazard ratios (HRs) (95% confidence intervals [CIs]) = 1.44 (1.01-2.06) and 0.97 (0.85-1.11), respectively (P interaction = .03). Similar findings were observed for hypothyroidism overall. Hypothyroidism overall vs euthyroidism was associated with greater mortality in Black participants (HR = 1.44 [95% CI = 1.03-2.03]) but not in non-Blacks (HR = 0.95 [95% CI = 0.83-1.08]) (P interaction = .03).
  
  
  CONCLUSIONS
  Among participants with CHF, subclinical hypothyroidism and hypothyroidism overall are associated with greater death risk. Additional studies are needed to confirm findings and explore possible mechanisms for the differential hypothyroidism-mortality association across race.
authors.affiliation: Renal Division, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA. crhee@partners.org
authors.forename: Connie M
authors.initials: CM
authors.lastname: Rhee
authors.forename: Gary C
authors.initials: GC
authors.lastname: Curhan
authors.forename: Erik K
authors.initials: EK
authors.lastname: Alexander
authors.forename: Ishir
authors.initials: I
authors.lastname: Bhan
authors.forename: Steven M
authors.initials: SM
authors.lastname: Brunelli
mesh_terms: D000328:Adult; D000368:Aged; D050197:Atherosclerosis / Q000401:mortality; D044383:Black People; D015331:Cohort Studies; D005260:Female; D006333:Heart Failure / Q000401:mortality*; D006801:Humans; D007037:Hypothyroidism / Q000150:complications / Q000208:ethnology / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies