The following is a summary of the study titled “Thyroid Function Status in Patients with Hypothyroidism on Thyroxine Replacement and Associated Factors: A Retrospective Cohort Study in Primary Care,” published in the October 2024 issue of Primary Care by Gunasekaran et al.

Effective long-term management of hypothyroidism involves monitoring thyroid function tests (TFTs) every six to twelve months, as outlined in clinical practice guidelines. For a study, researchers aimed to evaluate thyroid function status during follow-up visits over two years for patients on thyroxine replacement, identify factors affecting their thyroid status, and determine the optimal monitoring intervals for TFTs.

They conducted a retrospective cohort study analyzing adults diagnosed with hypothyroidism based on their electronic health records from polyclinics. Data were collected between July 2017 and June 2020, with follow-up thyroid status classified as under-replacement (TSH ≥ 3.70 mIU/L), over-replacement (TSH ≤ 0.65 mIU/L), or euthyroid (TSH 0.65–3.70 mIU/L). Demographic, clinical, and TFT data were analyzed statistically during the two-year follow-up, and stepwise logistic regression identified factors linked to suboptimal thyroid control. Kaplan-Meier analysis compared thyroid function status based on the intervals of TFT monitoring.

The analysis included 5,749 participants (mean age 62.1 ± 13.29 years; 79% female; 79.7% Chinese). After two years, 61.9% (n = 3,558) of the subjects were euthyroid, while 29.5% (n = 1,694) experienced under-replacement and 8.6% (n = 497) had over-replacement. No significant differences in thyroid status were observed based on dosing regimens (p = 0.193). Logistic regression indicated that under-replacement was significantly associated with male gender (AOR = 1.25, 95% CI = 1.03–1.51, p = 0.02) and obesity (AOR = 1.34, 95% CI = 1.08–1.66, p = 0.008). Each unit increase in the mean daily thyroxine dose correlated with a 2.72-fold increase in the odds of over-replacement.

When comparing monitoring intervals of 13-24 months to shorter intervals (≤ 12 months), the study found that shorter monitoring intervals were less effective in detecting thyroxine under-replacement (AOR = 0.57, 95% CI = 0.44–0.74, p < 0.001) and over-replacement (AOR = 0.62, 95% CI = 0.41–0.97, p = 0.033). Among the 3,312 adults who were euthyroid at baseline, the rates of developing abnormal thyroid function were 22.2%, 41.7%, and 59.6% at 6, 12, and 24 months, respectively, according to the Kaplan-Meier analysis.

The study revealed that approximately 60% of patients achieved euthyroid status with thyroxine replacement over two years. Thyroxine under-replacement was significantly associated with male gender and obesity. Additionally, the proportion of patients with euthyroid progressing to abnormal thyroid function doubled with TFT monitoring conducted at varied month intervals.

Source: bmcprimcare.biomedcentral.com/articles/10.1186/s12875-024-02613-z