The common practice of prescribing levothyroxine sodium to improve thyroid function among patients with subclinical thyroid disease may increase the potential for overtreatment, according to data in a United Kingdom-based retrospective cohort study.

Peter N. Taylor, MSc, MRCP, of the Cardiff University School of Medicine, and colleagues used data from the United Kingdom Clinical Practice Research Datalink to assess the trends in thyroid-stimulating hormone levels at the beginning of levothyroxine therapy and the risk for developing TSH suppression after treatment. The dataset included more than 52,000 patients who were given a prescription for the drug between January 2001 and October 2009, according to data.

“Overall, 30% of people were treated for levels of thyroid hormone deficiency potentially below those recommended in national guidelines, equivalent to 190,000 people in the UK. In addition, when thyroid blood levels were rechecked after 5 years on treatment, more than 1 in 10 people on levothyroxine were being overtreated,” Taylor told Endocrine Today.

Median TSH levels at the beginning of levothyroxine treatment decreased from 8.7 mIU/L to 7.9 mIU/L from 2001 to 2009, according to data. Five years after levothyroxine was initiated, 5.8% of patients displayed a TSH level of <0.1 mIU/L.

In 2009, patients with TSH levels of ≤10 mIU/L were prescribed levothyroxine more frequently compared with those treated in 2001 (OR=1.30; 95% CI, 1.19-1.42), according to data.

Between 2001 and 2006, there was a 1.81-fold increase in the rate of index levothyroxine prescriptions, researchers wrote. After adjustments for age, data revealed that there was still a 1.79-fold increase in the rate of index levothyroxine prescriptions.

Furthermore, older patients and those with cardiovascular disease risk were more likely to undergo levothyroxine treatment with TSH levels ≤10 mIU/L, according to researchers.

Moreover, patients with depression or tiredness at baseline showed an increased likelihood for developing TSH-suppression, unlike patients with CVD risk factors (ie, atrial fibrillation, diabetes, hypertension and raised lipids), researchers wrote.

The American Thyroid Association guidelines currently recommend levothyroxine therapy at TSH levels ≤10 mIU/L, when there are clear symptoms of hypothyroidism, positive thyroid autoantibodies, or signs of atherosclerotic CVD or heart failure.

“Taken together, this indicates that not only has the number of people being tested and treated for low thyroid hormone levels increased, but the majority of people nowadays are starting thyroid hormone for minor levels of underactivity for which we have no clear evidence of benefit,” Taylor said. “Studies are urgently required to clarify the risk vs. the benefits of exposing such a large number of these people to long-term thyroid hormone therapy.” – by Samantha Costa

Soure: Endocrine Today