Ute Eppinger
October 05, 2023
Thyroxine and L-thyroxine are two of the 10 most frequently prescribed medicinal products. “One large health insurance company ranks thyroid hormone at fourth place in the list of most-sold medications in the United States. It is possibly the second most commonly prescribed preparation,” said Joachim Feldkamp, MD, PhD, director of the University Clinic for General Internal Medicine, Endocrinology, Diabetology, and Infectious Diseases at Central Hospital, Bielefeld, Germany, at the online press conference for the German Society of Endocrinology’s hormone week.
The preparation is prescribed when the thyroid gland produces too little thyroid hormone. The messenger substance thyroid-stimulating hormone (TSH) is used as a screening value to assess thyroid function. An increase in TSH can indicate that too little thyroid hormone is being produced.
“But this does not mean that an underactive thyroid gland is hiding behind every elevated TSH value,” said Feldkamp. Normally, the TSH value lies between 0.3 and 4.2 mU/L. “Hypothyroidism, as it’s known, is formally present if the TSH value lies above the upper limit of 4.2 mU/L,” said Feldkamp.
Check Again
However, not every elevated TSH value needs to be treated immediately. “From large-scale investigations, we know that TSH values are subject to fluctuations,” said Feldkamp. Individual measurements must therefore be taken with a grain of salt and almost never justify a therapeutic decision. Therefore, a slightly elevated TSH value should be checked again 2-6 months later, and the patient should be asked if they are experiencing any symptoms. “In 50%-60% of cases, the TSH value normalized at the second checkup without requiring any treatment,” Feldkamp explained.
The TSH value could be elevated for several reasons:
Fluctuations depending on the time of day. At night and early in the morning, the TSH value is much higher than in the afternoon. An acute lack of sleep can lead to higher TSH values in the morning.
Fluctuations depending on the time of year. In winter, TSH values are slightly higher than in the summer owing to adaptation to cooler temperatures. Researchers in the Arctic, for example, have significantly higher TSH values than people who live in warmer regions.
Age-dependent differences. Children and adolescents have higher TSH values than adults do. The TSH values of adolescents cannot be based on those of adults because this would lead to incorrect treatment. In addition, TSH values increase with age, and slightly elevated values are initially no cause for treatment in people aged 70-80 years. Caution is advised during treatment, because overtreatment can lead to cardiac arrhythmias and a decrease in bone density.
Sex-specific differences. The TSH values of women are generally a little higher than those in men.
Obesity. In obesity, TSH increases and often exceeds the normal values usually recorded in persons of normal weight. The elevated values do not reflect a state of hypofunction, but rather the body’s adjustment mechanism. If these patients lose weight, the TSH values will drop spontaneously. Slightly elevated TSH values in obese people should not be treated with thyroid hormones.
The nutritional supplement biotin (vitamin H or vitamin B7), which is often taken for skin, hair, and nail growth disorders, can distort measured values. In many of the laboratory methods used, the biotin competes with the test substances used. As a result, it can lead to falsely high and falsely low TSH values. At high doses of biotin (eg, 10 mg), there should be at least a 3-day pause (and ideally a pause of 1 week) before measuring TSH.
Hasty Prescriptions
“Sometimes, because of the assumption that every high TSH value is due to sickness-related hypothyroidism, thyroid hormones can be prescribed too quickly,” said Feldkamp. This is also true for patients with thyroid nodules due to iodine deficiency, who are often still treated with thyroid hormones.
“These days, because we are generally an iodine-deficient nation, iodine would potentially be given in combination with thyroid hormones, but not with thyroid hormones alone. There are lots of patients who have been taking thyroid hormones for 30 or 40 years due to thyroid nodules. That should definitely be reviewed,” said Feldkamp.
When to Treat?
Feldkamp does not believe that standard determination of the TSH value is sensible and advises that clinicians examine patients with newly occurring symptoms, such as excess weight, impaired weight regulation despite reduced appetite, depression, or a high need for sleep.
If there are symptoms, the thyroid function must be clarified further. “This includes determination of free thyroid hormones T3 and T4, detection of antibodies against autologous thyroid tissue such as TPO-Ab [antibody against thyroid peroxidase], TG-Ab [antibody against thyroglobulin], and TRAb [antibody against TSH receptor], and ultrasound examination of the metabolic organ,” said Feldkamp. Autoimmune-related hypothyroidism (Hashimoto thyroiditis) is the most common cause of an overly high TSH level.
Treatment should take place in the following situations:
In young patients with TSH values > 10 mU/L;
In young (< 65 years) symptomatic patients with TSH values of 4 to < 10 mU/L;
With elevated TSH values that result from thyroid surgery or radioactive iodine therapy;
In patients with a diffuse enlarged or severely nodular thyroid gland; and
In pregnant women with elevated TSH values.
This article was translated from Medscape’s German Edition.
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