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 Dr. 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 Dr. 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 Dr. 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,” Dr. 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.