Context: Subclinical thyroid dysfunction and anemia are common disorders, and both have increasing prevalence with advancing age.

Objective: The aim of this study was to assess whether levothyroxine treatment leads to a rise in hemoglobin levels in older persons with subclinical hypothyroidism.

Methods: This preplanned combined analysis of 2 randomized controlled trials included community-dwelling persons aged 65 years and older with subclinical hypothyroidism who were randomly assigned to levothyroxine or placebo treatment. The levothyroxine dose was periodically titrated aiming at thyroid stimulating hormone (TSH) level within the reference range, with mock titrations in the placebo group. The main outcome measure was the change in hemoglobin level after 12 months.

Results: Analyses included 669 participants (placebo n = 337, levothyroxine n = 332) with a median age of 75 years (range, 65-97) and mean baseline hemoglobin of 13.8 ± 1.3 g/dL. Although levothyroxine treatment resulted in a reduction in TSH from baseline after 12 months of follow-up compared with placebo, the change in hemoglobin level was not different between the levothyroxine and the placebo groups (-0.03 g/dL [95% CI, -0.16 to 0.11]). Similar results were found in stratified analyses including sex, age, or TSH levels. No difference in change of hemoglobin levels after 12 months was identified in 69 participants with anemia at baseline (-0.33 g/dL [95% CI, -0.87 to 0.21]).

Conclusion: In persons aged 65 years and older with subclinical hypothyroidism, treatment with levothyroxine does not lead to a rise in hemoglobin levels, regardless of the presence of anemia.