Frequency and Determinants of Levothyroxine Therapy Initiation for Veterans with Subclinical Hypothyroidism

<b>Background/Objectives:</b> There is evidence of overtreatment in patients with subclinical hypothyroidism (SCH). We aimed to identify the proportion of patients treated for SCH and the determinants of thyroid hormone therapy initiation. <b>Methods:</b> We included a random sample of adult Veterans diagnosed with SCH from 1 January 2016 to 31 December 2018 and conducted univariate and multivariable logistic regression to identify factors associated with levothyroxine initiation. <b>Results:</b> Out of 229 Veterans with SCH [90.0% male, 87.2% White, 99.1% non-Hispanic, median age (interquartile range; IQR) 68 (17) years], 27.5% were treated with levothyroxine. The treated group had a higher proportion of White patients (95.2% vs. 84.2%, <i>p</i> = 0.039), a higher thyrotropin level [median (IQR), 6.98 (2.06) mIU/L vs. 6.14 (1.10) mIU/L, <i>p</i> = 0.0002], a higher proportion of patients with thyrotropin level ≥ 10 mIU/L (11.1% vs. 3.0%, <i>p</i> = 0.021), a lower frequency of confirmatory thyroid testing before initiating levothyroxine (49.2% vs. 97.0%, <i>p</i> < 0.0001), and a similar frequency of thyroid autoimmunity testing (3.2% vs. 0.6%, <i>p</i> = 0.18) compared to the untreated group. In a multivariable logistic regression analysis, White race (OR = 4.50, 95% CI 1.19 to 17.08, <i>p</i> = 0.026) and index thyrotropin level [OR = 1.71, 95% CI 1.24 to 2.35, <i>p</i> = 0.001; for every SD increase (1.6 mIU/L)] were associated with higher odds of treatment. <b>Conclusions:</b> Three in 10 Veterans with SCH received levothyroxine, often based on a single abnormal thyroid test without autoimmunity assessment. White race and higher thyrotropin level were linked to increased odds of starting treatment, indicating potential disparities and the influence of SCH severity on decision-making.