FRI521 Low FT3 And Decline In FT3 Levels Are Associated With Mortality; A Big-data Study

Disclosure: D.M. Strich: None. A. Israel: None. D.J. Gillis: None. Importance : If low free triiodothyronine levels could detect people at risk for early mortality, this could be helpful in focusing preventive medicine efforts on those who are in most need. Objectives: Thyroid hormone levels characteristic of "euthyroid sick syndrome" are seen in acute illness. Lower levels of free tri-iodothyronine and free thyroxine are seen with increasing age. We aimed, adjusting for normal age-associated decline of these hormones, to determine whether thyroid hormone levels could predict long-term survival. Design & Setting: This is a "big-data" study based on thyroid function tests from samples taken between 2008-2014. Data were crossed with electronic health records for morbidity and national death registry for mortality. Excluded: age below 18 years or above 95 years, taking thyroid or anti-thyroid drugs. We converted each measurement to an Age and Gender Adjusted Percentile (AGAP). We assessed survival according to ranges of initial AGAPs of Free Triiodothyronine (FT3), Free Thyroxine (FT4), and Thyrotropin (TSH) up to 8 years prior to death for two subgroups: "not healthy" - subjects with at least one of five chronic conditions registered in their electronic health chart; "healthy" - all others. The hazard ratio for death of various AGAPs was defined for the entire cohort and the subgroups separately. Results: Thyroid function tests were taken from 365,965 patients. 258,695 remained after exclusion criteria: 151,868 "not healthy" and 106,827 "healthy". After a median follow-up of 6.8 years, 5,865 /151,868 (10.4%) of the "not healthy" had died and 2,504/106,827 (2.3%) of "healthy" participants. The lowest 5(th) percentile initial FT3 AGAPs survival compared to the 95(th) percentile was for "not healthy" hazard ratio 5.71 (CI - 5.23 to 6.26, p<0.001), for "healthy" - hazard ratio was 3.92 (CI - 3.06 to 5.02, p<0.001)). Eight year survival associated with decline in FT3 AGAPs for 34,129 individuals was lowest for those with greater that 50%, decline: 86% of "not healthy" subjects and 95.5% of "healthy" subjects with such a decline survived 8 years. Conclusion and relevance: Lower age-adjusted values of FT3 were associated with decreased survival. This marker may potentially be used for focusing patients with expected reduced survival. Presentation: Friday, June 16, 2023