TSH stands for thyroid stimulating hormone. It is secreted by pituitary gland. As the name suggests, the main function of TSH is to stimulate the thyroid gland to secrete the hormones T3 and T4 which regulate the metabolism in the human body. TSH is often tested when metabolic irregularities are found in a person. The diagnosis of thyroid problems is often based on the results of this test. However, this may not be the most reliable way of detecting a thyroid malfunction, as there are lot of complications involved in the evaluation of test results.
Low TSH Levels
There is a lot of confusion regarding the normal TSH levels, as the standard reference scale varies in every country. In UK, a TSH level between 0.5 to 5.5 is considered normal. This same scale was followed in the US until 2003, after which the American laboratories revised the scale. As per the new American standards, TSH levels between 0.3 to 3.3 are considered as normal. However, some labs in the US still follow the old reference scale, which increases the ambiguity. This also results in non-uniformity in the treatment throughout the country. To add to the confusion, the TSH levels vary extensively throughout the day. The variation is about 2 points, which may influence the test results. TSH levels are minimum at noon and go on increasing after evening. Highest TSH levels are recorded at midnight, when the person is sleeping.
Many people expect their doctors to increase their thyroid dose, when their test results show lower TSH levels. However, to the surprise of the patient, the doctors lower the dosage of thyroid. When your test results show lower than normal TSH levels, it is an indication that your thyroid gland is already overworking and needs no further stimulation. Thus, below normal TSH level means a hyperactive thyroid gland or hyperthyroidism. This is the reason your doctor actually lowers your thyroid dose, when you have low TSH levels. Similarly, high TSH levels indicate the under-performance of thyroid gland or hypothyroidism.
Most doctors often rely solely on the TSH test results. They rarely ask the patient to go for T3 and T4 tests. This may not be an ideal practice always, considering the fact that TSH is not the secretion of thyroid gland itself but another gland (pituitary). Thus, if there is a problem with the pituitary gland itself, then the test evaluations may prove to be useless. Pituitary gland is controlled by hypothalamus, in the brain. There is a possibility that pituitary gland may unnecessarily increase or decrease TSH secretion, even though the thyroid gland might be functioning normally. Or sometimes, the exact opposite may also be possible, i.e the pituitary gland may under-secrete TSH even though the thyroid gland may have been under-performing. This may lead to false diagnosis of hyperthyroidism. In such cases, the patient may be taken off his thyroid medication to further lower the thyroid function. This can be extremely hazardous. Therefore, it is necessary to couple TSH test with T3 and T4 tests as well.
Causes, Symptoms, and Treatment
Causes: Grave's disease remains the prime cause of lower TSH levels. Nodular thyroid disease is another common cause of TSH levels that are below normal range. Rarely, inflammation of thyroid gland or thyroiditis may also lead to drop in TSH levels.
Symptoms: The symptoms of low TSH levels correspond to the symptoms of hyperthyroidism. This includes fatigue, palpitations, nervousness, insomnia, increased bowel movements, trembling hands, weight loss, muscle weakness, hair loss, etc.
Treatment: Lower TSH levels can be corrected with certain anti-thyroid medications, which control the functioning of thyroid gland. Radioactive iodine, which shrinks the thyroid gland can also be used to curb the hyperactivity of this gland. In some cases, hormone replacement therapy may be of great use. Proper diet also goes a long way in maintaining normal thyroid levels. Rarely, a surgery to partially remove thyroid gland can be recommended. People who cannot take anti-thyroid medications are often the candidates for this surgery.
As mentioned above, low TSH level indicate a possibility of hyperthyroidism. Therefore, most probably your doctor will ask you to undergo the treatment for same. However, always confirm that the TSH test results are indeed reliable and if there is a need to go for other thyroid tests.