Correlation Between Free Thyroxine Levels and Mortality in Hypertensive Patients

<b>Objective:</b> To study the link between free thyroxine (FT4) levels and mortality in hypertensive patients. <b>Methods:</b> Utilizing data from the National Health and Nutrition Examination Survey performed in the United States from 2007 to 2012. <b>Results:</b> This study included 3365 adults from the National Health and Nutrition Examination Survey (NHANES) 2007-2012. Weighted Cox regression model, Kaplan-Meier (KM) survival analysis, and restricted cubic spline (RCS) were used to analyze the link between FT4 levels and mortality in hypertensive patients. Furthermore, subgroup analyses and interaction analyses were carried out to evaluate the stability of links between FT4 levels and all-cause mortality across different subgroups of hypertensive patients. In the weighted Cox regression model, after adjusting for all covariates, FT4 levels treated as a continuous variable were positively linked to all-cause mortality in hypertensive patients (HR = 1.08,95% CI: 1.04-1.12, <i>P </i>< .001). When FT4 levels were treated as a categorical variable according to quartiles, the fully adjusted model found that the highest quartile of FT4 posed a greater all-cause mortality risk in hypertensive patients relative to the lowest quartile (HR = 1.47, 95% CI:1.01-2.15, <i>P </i>= .045). Based on the Kaplan-Meier survival curve, all-cause mortality was notably higher in groups Q3 and Q4 relative to FT4 levels in groups Q1 and Q2 (<i>P </i>< .001). The RCS curve revealed that the all-cause mortality in hypertensive patients exhibited a nonlinear increasing trend with rising FT4 levels (<i>P</i> for nonlinear = .033). The results were further validated by subgroup and sensitivity analyses, which confirmed their robustness and reliability. <b>Conclusion:</b> The level of FT4 is strongly linked to the all-cause mortality risk in hypertensive patients.