Abstract

Objective

To assess the associations between the mean thyrotropin (TSH) and mean free thyroxine (FT4), detected during follow-up, and mortality in a group of older euthyroid patients according to age-specific reference range (as-RR) for TSH.

Method

Retrospective survival analysis cohort including euthyroid elderly patients who were being monitored at the outpatient clinic of a university hospital from 2010 to 2013. All participants had been assessed for the risk of functional disability as a criterion for admission to this outpatient clinic. Mean TSH and FT4 values were calculated using hormone dosages obtained during the follow-up period. Each as-RR for TSH was divided into four equal parts, considering the lower levels as the main exposure variable (≤1.75 mlU/L for <80, and ≤2.0 mlU/L for ≥80 years). FT4 levels were explored according to two categories (< e ≥1.37 ng/dL). The outcome was time to death. We used Cox proportional hazard regression to estimate the hazard ratio (HR) and 95% confidence interval (CI).

Results

285 participants (73% females, mean age =80.4 years) followed by a median of 5.7 years (IQR =3.7–6.4; maximum =7), of which 114 died. After the adjusted final model, mortality was associated with the lowest mean TSH (HR=1.7; CI=1.1–2.7; p=0.016) and with the upper mean of FT4 (HR=2.0; CI=1.0–3.8; p=0.052).

Conclusions

Higher FT4 and lower TSH mean levels were associated with risk of death in a cohort of euthyroid older adults using an as-RR of TSH.

Keywords
Thyroid hormones; Geriatric assessment; Mortality