Age and Gender Adjusted FT3 Levels as Novel Predictors of Survival

David Strich, Ariel Israel, Shalom Edri, David Gillis
The Journal of Clinical Endocrinology & Metabolism, Volume 108, Issue 12, December 2023, Pages 3295–3301
https://doi.org/10.1210/clinem/dgad342

Abstract

Context

Lower levels of free T3 (FT3) occur during acute illness, as part of “euthyroid sick syndrome.” A chronic form of this syndrome also exists.

Objective

To determine whether thyroid hormone levels predict long-term survival.

Design and Setting

This was a “big-data” study of thyroid function tests from samples taken between 2008 and 2014. Data were crossed with electronic health records for morbidity and mortality. Test results were converted to age- and gender-adjusted percentiles (AGAPs). The hazard ratio for death was crossed with ranges of initial AGAPs and change in AGAPs for 2 subgroups: “not healthy” (subjects with at least 1 of 5 chronic conditions registered in their electronic health chart) and “healthy” (all others).

Participants

2,453,091 sets of thyroid function tests from 365,965 distinct patients were evaluated. 258,695 sets remained after excluding patients registered as taking thyroid preparations or anti-thyroid drugs.

Main Outcome Measure

Hazard ratio for death, planned before data collection.

Results

The cohort included 151,868 not healthy and 106,827 healthy people. After a median 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. Low initial FT3 AGAPs were predictive of poor survival. The hazard ratio for survival compared between the lowest 5 and highest 50 percentiles of initial FT3 AGAPs for not healthy participants was 5.71 [confidence interval (CI) 5.23–6.26, P < .001] and for healthy was 3.92 (CI 3.06–5.02, P < .001).

Conclusion

Low FT3 AGAPs predicted poor survival, most strongly among not healthy people.

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