Elevated TSH in adults treated for hypothyroidism is associated with increased mortality

Abstract

Context Numerous studies investigated the link between hypothyroidism and mortality, but a definite conclusion is hard to reach as these were limited by a number of factors, including age of participants, comorbidities and single measurement of thyroid function. Objective To evaluate the association between TSH and fT4 levels and mortality in patients with levothyroxine-treated hypothyroidism. Design and setting Observational data of hospitalized patients (2011–2014). TSH and fT4 levels obtained between at least 30 days after discharge and until death or end of follow-up were collected. Median TSH and fT4 levels were stratified into categories. Patients In total, 611 patients with treated hypothyroidism, aged 60–80 years (72% females, mean age 71 ± 6 years) were included in the study. Main outcome measure All-cause mortality up to 66 months after discharge, by TSH and fT4 categories. Results During follow-up, the average numbers of TSH and fT4 measurements were 5.5 ± 3.8 and 2.5 ± 4.2 per patient respectively. Mortality rates were 28%, 29% and 54% with median TSH of 0.5–2.5, 2.5–5.0 and 5.0–10.0 IU/L respectively. Adjusted hazard ratios for mortality with median TSH between 5.0 and 10.0 IU/L were 2.3 (95% CI: 1.6–3.4) and 2.2 (95% CI: 1.6–3.2) compared with patients with TSH between 0.5–2.5 IU/L and 2.5–5 IU/L respectively. There was no difference in mortality between patients with median fT4 10–15 or 15–20 pmol/L. Conclusion In treated hypothyroid adult patients and serial measurements of thyroid function tests, median TSH levels of 5–10 IU/L are associated with increased mortality with no effect of fT4 levels. Treatment should aim at achieving euthyroidism to improve survival.