Gh Impact On Thyroid Hormone Receptors
An additional mechanism which could be involved in thyroid hormone balance disorders after rhGH therapy is its impact on thyroid hormones receptors. The presence of thyroid hormone receptors in growth plates is well known . Susperreguy et al. reported that the individual growth response in patients with idiopathic short stature treated with rhGH correlated positively with the change in the TR mRNA level and negatively with the TR mRNA level. The design of the study was based on the evaluation of mRNA of TRs in peripheral blood mononuclear cells however there was a parallel evaluation of serum sex hormone binding globulin which, reflects the effect of thyroid hormones on the liver, and also osteocalcin and b-cross laps, which are serum biochemical markers reflecting thyroid hormone action at the bone tissue. The authors reported that the higher increase in TR1 and TR2 mRNAs levels after 12 months of GH treatment was positively correlated to the gain of growth velocity and bone markers. Moreover, they observed a better gain in growth velocity in response to GH therapy in the individuals who had the higher increase of TR1 mRNA level . This finding is in line with the main role of TR1 in bone longitudinal growth and suggests a possible direct influence of GH on thyroid hormone receptors in the growth plate.
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
What Affects The Test
Reasons the interpretation of your test may be affected:
- Taking certain medicines, such as:
- Corticosteroids, estrogen, progesterone, or birth control pills.
- Antiseizure medicines such as phenytoin or carbamazepine.
- Heart medicines such as amiodarone or propranolol.
- Thyroid Biopsy.
- Other blood tests are often used to check how well the thyroid gland is working.
- Because false-positive results can occur when testing a newborn for congenital hypothyroidism, the thyroid hormone tests may be repeated a few days after initial testing. If the results are still abnormal and congenital hypothyroidism is suspected, additional testing is done.
- Thyroid-stimulating hormone test measures the amount of TSH in the blood and is considered the most reliable way to find a thyroid problem. If the TSH test is abnormal, other thyroid hormone tests such as a FT3 or FT4 may be done. For more information, see the topic Thyroid-Stimulating Hormone.
- Thyroid antibodies test measures the presence of antibodies against thyroid tissue. Antibodies may mean that you have an autoimmune disease such as Hashimoto’s thyroiditis or Graves’ disease.
- Other tests used to investigate problems with the thyroid gland include:
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What To Think About
- The thyroid-stimulating hormone test is the best screening test for conditions that can affect the thyroid gland.
- If the TSH results are abnormal, the results of a TSH test should be considered along with the results of thyroid hormone tests, especially free thyroxine results. To learn more about FT3 and FT4 testing, see the topic Thyroid Hormone Tests.
Testing Your Thyroid Levels
According to the American Thyroid Association, there isnt one test for every situation in fact, there are several kinds of thyroid tests. But if you are concerned about thyroid issues, or if your hormones are imbalanced, your doctor may provide an initial TSH level blood test. This is because the TSH level can serve as a tip-off to other, more specific issues.Whats a normal TSH level? Most lab companies have a wide reference as it relates to TSH levels , Dr. Rice says. So, if your results are somewhere between 0.4-4.0, youd be in the normal range. However, there is research that suggests that the reference range for TSH should be narrowed to 0.4 to 2.5, says Dr. Rice, which means that the normal range could be even smaller than some healthcare providers might think.Generally, healthy TSH levels are an indicator the whole system is working well, but thats an oversimplification at best. A normal T3 level might be somewhere between 100 to 200 nanograms per deciliter , while a normal T4 level falls between 5.0 to 12.0 micrograms per deciliter . Free T4, which tests for the amount of T4 that is available in the body, should range between 0.8 to 1.8 nanograms per deciliter .
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Questions To Ask Your Endocrinologist:
- What tests do I need to check my thyroid levels?
- What are the normal ranges for each hormone?
- Are my T3, T4, and TSH levels normal?
- Are my symptoms indicative of a thyroid disorder?
- How can we correct any issues with the levels through medication or lifestyle changes?
- Are there any side effects to the medications?
- How long does it take before the medicine starts to work?
Thyroid Medications During Pregnancy
If you have a high TSH then there are special changes that you must make once you know you are pregnant.
These changes include increasing your dose of thyroid medication immediately upon finding out or suspecting you are pregnant.
Because your child, especially during the early stages of development, is reliant upon your thyroid hormone until it can produce its own thyroid hormone.
During the first trimester, your child will be relying upon your thyroid gland for its thyroid hormone.
And, if you are taking thyroid medication your ability to produce thyroid hormone is limited.
This is why most doctors recommend that you increase your dose of thyroid medication anywhere from 20 to 50% .
In fact, this recommendation applies even if you miss or skip a period and suspect you might be pregnant.
The most critical time in development often occurs before you even know that you are pregnant.
Because of this, it’s very important that you pay attention to your body and try to find out if you are pregnant as early as possible.
But does that mean you can’t use other thyroid medications?
Not at all.
Instead of focusing on which medication you use, you should focus on your thyroid lab tests and how you are feeling.
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What Is The Reason For High Tsh Levels
High levels typically indicates an underactive thyroid gland, which produces too little thyroid hormone. This is known medically as hypothyroidism.
Common causes of hypothyroidism include an autoimmune disease , radiation treatment, or surgical removal of the thyroid gland.
Replacing thyroid hormone and altering your diet are crucial for the safe and effective treatment of an underactive thyroid.
Summary: High TSH levels for the average adult are 4.2 mIU/L and over. This reading typically indicates an underactive thyroid.
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Physiologic Issues In Assessing Tsh Values
Considerable literature exists regarding what the normal range for TSH really should be, and this topic is covered at length in recent reviews, and in clinical guidelines for the diagnosis and management of hypothyroidism., Indeed, even though the normal range for TSH is generally listed at between 0.35 mIU/mL and 4.50 mIU/mL, it is likely that the most normal range is between 0.5 mIU/mL and 2.50 mIU/mL. It is for this reason that the target TSH in the management of hypothyroidism is within this latter range., Note that the goal range for replacement therapy is different than the range at which hypothyroidism is diagnosed dose, it does not warrant initiation of replacement therapy in a non-pregnant patient). The mean inter-assay precision for the TSH measurement is generally good. The method used at our institution has a precision of ~3.2%, indicating that variations in the result over time in a single patient are not likely to be related to the assay itself but rather to other factors . Lastly, it is important to understand that normal ranges are calculated based on the 2.5th to 97.5th percentiles of the distribution of values measured in the population tested. Therefore, 2.5% of people with completely normal thyroid function will have a TSH slightly below the listed normal range .
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Questions For Your Doctor About Test Results
When you review the results of your TSH test with your doctor, it could be helpful to ask specific questions, such as the following:
- Is my level of TSH within the normal range?
- Do my test results suggest that my thyroid is overactive or underactive?
- What additional tests will you be ordering, if any?
When Levothyroxine Administration Is A Necessity
Thyroxine is secreted by the thyrocytes and is the main thyroid hormone in the circulation. Thyroxine is actively transported to the various organs where it is converted to triiodothyronine by the activity of the deiodinases . Triiodothyronine, the active form of thyroid hormone, is secreted in small amounts by the thyroid but is mainly generated via extrathyroidal conversion of the prohormone thyroxine. Hypothyroidism is a common endocrine disease that requires timely and lifelong treatment since, if left untreated, it can contribute to hypertension, dyslipidaemia, and heart failure and induce reversible dementia and infertility, as well as neurosensory, musculoskeletal, and gastrointestinal symptoms . There is currently no other treatment for hypothyroidism, other than providing thyroid hormone replacement. Due to its long half-life of about 7 days, in patients in the clinically euthyroid state, levothyroxine is the preferred first-line treatment for primary hypothyroidism and has been the most commonly prescribed treatment since the 1980s .
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Thyroxine Triiodothyronine And Tsh Levels
The main job of the thyroid gland is to make the hormone thyroxine, also known as T4 because it has four iodine molecules. The thyroid also makes the hormone triiodothyronine, known as T3 because it has three iodine molecules, but in smaller amounts, explains Cathy Doria-Medina, MD, an endocrinologist with HealthCare Partners Medical Group in Torrance, California. The thyroid gland makes mostly T4, the T4 has to be converted to T3, because T3 is the part of thyroxine that actually does the work, she says.
The pituitary gland at the base of the brain controls hormone production in your body. It makes thyroid-stimulating hormone , which tells the thyroid gland how much T4 and T3 to produce. The TSH level in your blood reveals how much T4 your pituitary gland is asking your thyroid gland to make. If your TSH levels are abnormally high, it could mean you have an underactive thyroid, or hypothyroidism. Thats because it indicates your pituitary gland is producing more TSH in an effort to stimulate your thyroid to produce thyroid hormone, according to the Mayo Clinic.
TSH levels go in the opposite direction of your thyroid hormone, Dr. Doria-Medina explains. If youre making too little thyroid hormone, your TSH will go up. If youre making too much thyroid hormone, your TSH will go down.
If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism.
What Does The Test Measure
The TSH test measures thyroid-stimulating hormone, which is a hormone that prompts the thyroid to produce other hormones. The thyroid is a butterfly-shaped gland in your neck that makes the hormones triiodothyronine and thyroxine . T3 and T4 control your metabolism, or how your body uses and stores energy.
Although TSH acts upon the thyroid gland by binding to the TSH receptor, it is made in the pituitary gland. The pituitary gland is sometimes called the master gland, because it produces many hormones that control the functions of other glands in the body. The pituitary gland is able to sense when your T3 and T4 hormone levels are too low or too high. In response, it will produce more or less TSH to stimulate your thyroid gland to produce the right amount of hormones.
If your thyroid is underactive, you may have high levels of TSH as your pituitary gland tries to stimulate the thyroid to produce more T3 and T4. If your thyroid is overactive, your TSH may be abnormally low because your pituitary gland stops making TSH when your thyroid hormone levels are too high.
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The Hpt Axis Suppression In The Patients Treated With Rhgh
Jørgensen et al. postulated the direct inhibitory effect of rhGH to pituitary circadian secretion of TSH levels. In line with this data is the lack of TSH increase associated with the decrease of fT4 observed in the majority of GHD patients treated with rhGH . These data are also supported by the study of Roelfsema et al. , wherein there were untreated patients with acromegaly who had reduced basal and pulsatile TSH secretion with lower amplitude. The authors explained this phenomenon by increased intracellular conversion of T4 into T3 in folliculo-stellate cells of the pituitary, which via biofeedback inhibits the synthesis of TSH beta-subunit and the secretion of mature TSH . This mechanism seems to be very attractive as the explanation of GHs effect on pituitary however, it should be taken into account that the levels of GH in acromegalic patients are much higher in comparison to GH substitution in GHD patients, in whom there should be guaranteed physiological GH/IGF-1 levels.
What Is A Tsh Test
Thyroid testsBlood tests to measure thyroid hormones are readily available and widely used. Not all thyroid tests are useful in all situations.
TSH TestThe best way to initially test thyroid function is to measure the TSH level in a blood sample. Changes in TSH can serve as an “early warning system” often occurring before the actual level of thyroid hormones in the body becomes too high or too low.
A high TSH level indicates that the thyroid gland is not making enough thyroid hormone . On the other hand, a low TSH level usually indicates that the thyroid is producing too much thyroid hormone . Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid . In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.
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What Should My Thyroid Levels Be To Get Pregnant
When it comes to optimal thyroid levels during preconception, this is unfortunately a topic that has been long debated. If you recently had your thyroid labs completed and you are not pregnant, you may notice that the normal range is anywhere from 0.4-4.5 milli-international units per liter. The problem with this range, especially during preconception, is that your thyroid is extremely important during the first few weeks of pregnancy. In fact, during the first 10 weeks of pregnancy your babys brain development relies solely on your thyroid function. This is why it is actually NORMAL for your thyroid function to increase during pregnancy. Once the baby reaches 10 weeks gestation, the babys thyroid gland is developed enough to begin to produce its own thyroid hormones.
That being said, the minute you are pregnant, your doctor will want to make sure your TSH stays between 0.5-2.5, NOT 0.4-4.0 as it was previously when you were not pregnant. So how come two weeks before you get pregnant a TSH of 3.5 is totally normal but then, the minute you get pregnant your doctor will likely give you a thyroid medication to get you to the optimal 2.5 range? This is where there is still much debate however, for my patients who come to see me during preconception, I generally aim for their TSH to be 0.5-2.5 so that we know that their thyroid is well supported and ready for a health pregnancy.
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How Does Our Thyroid Affect Fertility
As you can see although hypo/hyperthyroidism often have opposing symptoms, they BOTH can cause menstrual irregularities. Menstrual irregularities including irregular cycles and anovulation can significantly impact your ability to get pregnant. Again, if you dont ovulate, you cant get pregnant. This is why proper comprehensive thyroid lab work 6-8 months BEFORE trying to conceive is something I recommend to all of my patients.
Low thyroid function, like that seen in hypothyroidism, can also lead to a decrease of serum FSH and LH . FSH and LH are the primary hormones released by the brain to stimulate your ovaries to ovulate. Without proper FSH and LH function, the ovaries cannot function properly.
Why It Is Done
A test for thyroid-stimulating hormone is done to:
- Find out whether the thyroid gland is working properly.
- An underactive thyroid gland can cause symptoms such as weight gain, tiredness, dry skin, constipation, a feeling of being too cold, or frequent menstrual periods.
- An overactive thyroid can cause symptoms such as weight loss, rapid heart rate, nervousness, diarrhea, a feeling of being too hot, or irregular menstrual periods.