Female Sex, TSH Levels Predict Odds of Subclinical Hypothyroidism Treatment

Female sex and index serum thyrotropin (TSH) levels among patients with subclinical hypothyroidism are associated with higher odds of thyroid hormone replacement therapy (HRT), according to study findings published in the journal Thyroid.

Levothyroxine has been a long-standing treatment for hypothyroidism; however, questions remain about whether levothyroxine is a viable treatment for subclinical hypothyroidism.

Researchers conducted an electronic health records-based observational cohort study that included adults diagnosed with subclinical hypothyroidism from 4 academic centers in the United States and Mexico from January 1, 2016 to December 31, 2018, identifying determinants of thyroid HRT for subclinical hypothyroidism and the frequency of treated subclinical hypothyroidism.

A total of 796 patients (mean age, 54.4 years; 65.2% women) with subclinical hypothyroidism were included in the study. Among the study participants, 75.9% were White and 87.3% were non-Hispanic.

Multivariable logistic regression was used to assess determinants of treatment, with adjustments for age, sex, thyroid symptoms, history of osteoporosis, history of arrhythmias, history of cardiovascular disease, index TSH level, and free thyroxine level.

A total of 165 patients received thyroid HRT (levothyroxine). The treated group had an index TSH level of 7.6 mIU/L compared with 6.0 mIU/L in the untreated group (n=631). The percentage of patients in the treated group with a TSH level of 10 mIU/L and higher was 11.5% compared with 3.2% in the untreated group. The confirmatory TSH level was the sole factor in determining levothyroxine treatment in this study.

In the treated group, only 46.7% of patients had confirmatory thyroid function tests before deciding to start thyroid HRT, compared with 65.6% in the untreated group.

Thyroid autoimmunity was tested in roughly 1 in 3 patients, an often-underused diagnostic. A positive thyroid autoimmunity test occurred in 48.2% of patients in the treated group, compared to 20.3% in the untreated group. Female sex (odds ratio [OR], 1.71; 95% CI, 1.13-2.59) and index TSH level (OR, 1.97; 95% CI, 1.56-2.49) were associated with higher odds of treatment.

There were several study limitations, including the inability for researchers to investigate whether patients’ thyroid function tests were checked prior to entering the study; selection bias and other factors could affect the outcome of the study; and using electronic health records for the study may have impacted the accuracy of the data.

“Among patients with SCH [subclinical hypothyroidism], female sex and index TSH level were associated with higher odds of treatment,” the researchers wrote. They concluded, “Further studies are needed to evaluate the appropriateness of thyroid hormone replacement therapy and whether those factors are associated with SCH overtreatment or can identify patients who might benefit from treatment.”