The thyroid-stimulating hormone is one of the hormones synthesized and secreted by the anterior pituitary gland. When secreted in the bloodstream, it stimulates the thyroid gland, an endocrine gland located in the neck area, to produce and secrete thyroid hormones; thyroxine and triiodothyronine, T4 and T3, respectively.
These thyroid hormones maintain bodily functions such as metabolism and digestion, body temperature, heart function, and blood pressure, as well as bone and muscle density.
Thyroid hormones once released and reached standard concentrations will send negative feedback to the anterior pituitary gland to stop secreting TSH so there is no surplus of said hormones. They will also send negative feedback to the hypothalamus to stop producing the thyrotropin-releasing hormone which is also responsible for stimulating the pituitary gland to release TSH. These two ways mechanisms keep the TSH level in check.
The normal TSH levels range is 0.5 mU/L to 5.0 mU/L, TSH levels charts may vary from one institution to another, and what is considered normal may depend on each individual’s physiological status, but the stated range may be considered as a general compass to assess thyroid activity.As a general rule, the TSH normal range for females is the same as for males and is only affected by pregnancy and a person’s age. Nonetheless, female patients are at increased risk of hormonal imbalance.
TSH in Pregnancy
The normal level of TSH in pregnancy is < 3.0 mU/L. During pregnancy, thyroid gland activity is markedly increased due to increased demand for thyroid hormones to carry out a healthy pregnancy with no risk for preterm delivery or miscarriage, and even for the mother’s well-being.
Implications of low TSH levels
When the thyroid-stimulating hormone is low, this signifies hyperactivity of the thyroid gland, referred to as hyperthyroidism. In hyperthyroidism, the thyroid gland excessively produces thyroid hormones which will constantly send negative feedback to reduce TSH release from the pituitary gland.Many common conditions cause the thyroid gland to become overactive like Grave’s disease, inflammation of the gland itself, multimodal Goiter, or an adenoma growing. Sometimes it happens when hypothyroidism treatment is too harsh, requiring a dose reduction to be resolved. In less common cases, the excess of thyroid hormones is secondary to a tumor in the thyroid gland.Low TSH symptoms comprise weight loss, anxiety, tremors, tachycardia, bulging of the eyes, poor sleeping hygiene, hirsutism, menstruation disturbances, more frequent bowel activity, and enlarged thyroid gland upon palpation.If left untreated for a long time, hypothyroidism may cause heart problems like arrhythmias and atrial fibrillations which can have detrimental effects on health. It may also lead to osteoporosis, loss of vision, or even a thyrotoxic crisis which is a life-threatening emergency.
Treatment of low TSH
To bring back normal TSH levels, different modalities may be employed depending on the patient’s age, concomitant conditions, and tolerability. This includes conventional oral medication, radiation, or surgery.
– Oral medication aims to target the thyroid and to relieve symptoms associated with hyperthyroidism. There are three antithyroid medications: Methimazole/Topazole, Carbimazole, and Propylthiouracil, and all directly halt the thyroid hormones production, leading to a boost in TSH secretion.
– They follow a daily regimen with a dose that will depend on the severity of the condition and will be maintained after reaching normal levels. Beta-blockers are added to antithyroid therapy to alleviate symptoms such as tachycardia and tremors.
– Another option is radioactive iodine therapy or ablation. The radioactivity from the orally administered iodine will directly destroy thyroid gland cells so fewer thyroid hormones are produced. It takes up to 18 weeks to reach full effectiveness, and sometimes therapy may require another course
– Surgery is a definitive cure for hyperthyroidism, reserved for patients who fail or cannot antithyroid and radioactive iodine therapies, and in those whose thyroid gland is too enlarged with a suspected malign tumor.
LH levels can sometimes fluctuate outside the normal range and will either decrease or increase, each having different causes and implications depending on the gender. Testing for LH level is done in concordance with FSH levels by drawing blood samples with lab kits. The test is ordered when the physician needs to investigate the reason behind irregular menstruation, inability to conceive, delayed or early puberty, or change in libido.
Implications of high TSH levels
When the thyroid-stimulating hormone is high, this indicates an under-activity of the thyroid gland, referred to as hypothyroidism. In hypothyroidism there are not enough thyroid hormones being produced by their gland, leading to excess production of TSH since the concentrations are not enough to trigger the negative feedback to the pituitary gland.
Hypothyroidism is the result of different disorders and conditions such as autoimmune diseases like Hashimoto’s disease, congenital hypothyroidism, damage to the thyroid gland due to chemotherapy or inflammation, or surgical removal of the thyroid gland for other underlying reasons. Hypothyroidism can sometimes be the result of hyperthyroidism treatment, in that case, treatment should be revised.
While a TSH level of more than 5.0 mU/L is considered abnormal, there is no consensus on what is considered a dangerously high TSH level due to differences in ranges both from a patient’s side and the institution’s standard. But naturally, an extremely high TSH reading will require a more rigorous and longer treatment.
High TSH levels symptoms include lethargy and fatigue, hoarseness, weight gain, feeling cold, hair loss, dry skin, constipation, irregular menstruation sometimes infertility, and bradycardia.
Treatment of high TSH
Levothyroxine is the drug of choice, it is a synthetic form of T4 thyroxine, hence will restore healthy levels of thyroid hormones to decrease TSH levels. Levothyroxine follows a daily regimen with a dose that will depend on TSH levels. The dose may be adjusted according to the change in TSH levels, at first every 6 weeks then every 6 months once stabilized.
To ensure treatment effectiveness, the medication should be taken on an empty stomach, at least half an hour before any food consumption, without skipping any dose preferably. Patients are also advised not to switch brands without consulting with their physicians due to slight differences in dosing between brands.
Levothyroxine is safe in pregnancy, and it is highly advised not to discontinue treatment for the sake of both the mother and the fetus health. In some cases, the dose of levothyroxine needs to be increased to meet increased demand.
The thyroid-stimulating hormone is a key hormone in the regulation of endocrine activity of the thyroid gland and all the physiological functions that are associated with it. Dysregulation in TSH levels is very common, with women being affected more than men. Luckily, treating both hyper and hypothyroidism is fairly simple and highly effective in patients.