What Is Thyroid Hormone
Thyroid hormone is made by the thyroid gland, a butterfly-shaped endocrine gland normally located in the lower front of the neck. Thyroid hormone is released into the blood where it is carried to all the tissues in the body. It helps the body use energy, stay warm and keeps the brain, heart, muscles, and other organs working as they should.
Thyroid hormone exists in two main forms: thyroxine and triiodothyronine . T4 is the primary form of thyroid hormone circulating in the blood . To exert its effects, T4 is converted to T3 by the removal of an iodine atom; this occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. T3 normally accounts for about 5% of thyroid hormone circulating in the blood.
Most thyroid hormone in the blood is bound by protein, while only a small fraction is “free” to enter tissues and have a biologic effect. Thyroid tests may measure total or free hormone 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.
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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What Is A Normal Tsh Level
TSH levels are measured in ranges. In general, the normal reference range for TSH levels is 0.5 to 5.0 milli-international units per liter of blood. A TSH reading in this range indicates the thyroid gland is functioning normally.
However, doctors do not all agree on the precise TSH range of a normal-functioning thyroid gland. Some doctors consider a TSH level of 4.5 mIU/L to be an indication of an underactive thyroid. Before diagnosing you with any type of , your doctor will consider not only your TSH level but any signs or symptoms youre exhibiting, such as an enlarged thyroid gland.
What Makes Tsh Fluctuate
The release of TSH is first stimulated by a hormone called TRH.
Once the thyroid stimulating hormone makes its way to your thyroid, levels are largely dictated by the amount of T3 and T4 in your blood.
When T3 and T4 levels are low, the body produces more TSH to stimulate the thyroid. But when T3 and T4 levels are high, the body produces less .
Image . Click to enlarge.
Several other factors can also influence TSH levels:
- Inflammation of the thyroid gland
Those with Graves disease have high low TSH and subsequent high thyroid hormone levels. Hashimotos disease is the opposite.
Summary: Low TSH typically;indicates excessive thyroid hormone levels, while high TSH indicates thyroid hormone deficiency.
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Is There Anything Else I Need To Know About A Tsh Test
Thyroid changes can happen during pregnancy. These changes are usually not significant, but some women can develop thyroid disease during pregnancy. Hyperthyroidism occurs in about one in every 500 pregnancies, while hypothyroidism occurs in approximately one in every 250 pregnancies. Hyperthyroidism, and less often, hypothyroidism, may remain after pregnancy. If you develop a thyroid condition during pregnancy, your health care provider will monitor your condition after your baby is born. If you have a history of thyroid disease, be sure to talk with your health care provider if you are pregnant or are thinking of becoming pregnant.
In People With Thyroid Disease
In people being treated for hypothyroidism, a low TSH level may mean:
- Overmedication with thyroid hormone replacement
- Interactions that cause increased absorption or activity despite an optimal dose of medication
- Central hypothyroidism
In people being treated for hyperthyroidism, a low TSH level usually means that further treatment is needed to reduce thyroid hormone levels.
It could also mean that a person must continue to be monitored to make sure thyroid hormone levels return to normal. This is often the case for people who have temporary thyroiditis related to pregnancy or chemotherapy treatment.
Treatment may need to be more aggressive
Medication may not be absorbing enough
Treatment may be more aggressive than needed
Medication may be absorbing too much
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Tsh Levels During Pregnancy
Thyroid hormones can affect brain and nervous system development of the baby, especially during the first trimester. At around 12 weeks, the baby will start to produce thyroid hormones of its own. Until then, the baby is entirely dependent on the transfer of thyroid hormones from the mother.
Untreated thyroid disease can cause miscarriage, premature birth, or low birth weight. It can also cause preeclampsia. Having an underactive thyroid during pregnancy can also affect the babys growth and brain development.
Its important to have your TSH levels checked during pregnancy to make sure that both you and your baby remain healthy.
Hormones secreted during pregnancy can affect TSH levels, altering them from your typical numbers.
This chart provides an overview of normal, low, and high TSH levels for pregnant women who are between 18 and 45 years old:
Having a doctor monitor your thyroid gland and its production of thyroid hormones is the only way to comprehensively determine thyroid health.
The thyroid is one of several glands and structures that make up the bodys endocrine system.
It works in partnership with the pituitary and hypothalamus glands. These glands stimulate the thyroid to secrete two hormones, which are then released into the bloodstream: T4 and T3.
When Do You Need Treatment
Many hypothyroid patients feel at their best when theyre on medication and their thyroid levels are in the optimal TSH range of 0.5-2.00 , Dr. Henderson says. Since lab assays and ranges vary, the optimized levels for a patients specific lab can also vary. For elderly patients, the TSH target is in the 4.0 6.0 range.;
Most doctors commonly treat their hypothyroid patients with a daily dose of levothyroxine , a man-made version of the T4 thyroid hormone made by the body, some doctors recommend using both T4 and T3 as the treatment option. ;
With thyroid medication, the dosing has to be just right, Dr. Henderson says. Too much or too little of the medication can lead to side effects that affect a patients health.
In patients who are diagnosed as hyperthyroid, treatment can include antithyroid medications such as methimazole, that works to control the overactive thyroid. Some patients are given radioactive iodine, which is given in pill form to gradually and safely shrink the thyroid.
If you are experiencing signs of an under- or overactive thyroid, seek professional medical advice from your doctor or a specialist in endocrinology about these tests and treatments.
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Reference Range & Interpreting Your Lab Results
How do you know if your antibody levels are optimal?
When it comes to TSI testing you’ll find that there is a standard “reference range”.;
This range is developed based on “normal” healthy adults and if you fall within this range you are considered to also be “normal”.;
But let’s break this down a little bit more:
If the presence of antibodies in your body mean that there is a chance that you may have an autoimmune disease, doesn’t it make sense to want this number as close to zero as possible?;
I would tend to agree with you on that, and therefore I tend to prefer when patients have a TSI level which as close to zero as possible.;
The standard range for TSI is measured as a percentage and the cut off for normalcy is usually less than 1.4 or 1.3 .
This means that you can have a result of 130% and still be considered “normal” even though you are rapidly approaching the high end of that range.;
The “high end” of the normal range is considered to be 140% which means that the closer you get to this range the closer you are to developing abnormal test results and the closer you are to a diagnosis of Graves’s disease.;
Because of this, it is preferable to have your percentage as far away from that “high end” as possible, in this case as far away from 140% as possible. ;
Thyroid Function Tests Associated with High TSI
If your TSI lab tests are abnormal then your doctor will also order several tests to identify the function of your thyroid gland.;
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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What Is Thyroid Stimulating Hormone
Thyroid-stimulating hormone is a hormone that stimulates the thyroid gland to produce thyroid hormones. The pituitary gland secretes more TSH when blood levels of T4 and T3 fall below normal, and reduces the TSH secretion when T4 and T3 levels rise. The hypothalamus region of the brain regulates pituitary gland activity.
How Is Thyroid Stimulating Hormone Controlled
When thyroid stimulating hormone binds to the receptor on the thyroid cells, this causes these cells to produce thyroxine and triiodothyronine and release them into the bloodstream.;These hormones have a negative effect on the pituitary gland and stop the production of thyroid stimulating hormone if the levels of thyroxine and triiodothyronine are too high.;They also switch off production of a hormone called thyrotropin-releasing hormone.;This hormone is produced by the hypothalamus and it also stimulates the pituitary gland to make thyroid stimulating hormone.;
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Do Antibodies Levels Correlate With Disease Progression
You might expect that higher levels of thyroid stimulating immunoglobulin may correlate with a worse clinical picture.;
The higher your antibodies become the more likely you are to experience the symptoms of hyperthyroidism.;
Unfortunately, this doesn’t always appear to be the case in every patient, but testing your antibodies frequently may be helpful in some instances.;
And some studies do show that there is a positive correlation between the severity of thyroid eye disease and the initial TSI level .
What does this mean?
It means that the higher your antibody level is at the time of diagnosis the more likely you are to develop thyroid eye disease.;
What is not known, however, is if your antibody level correlates with more severe symptoms of hyperthyroidism .;
It seems that some of your thyroid tissue tends to be less responsive to TSI stimulation based on the fact that some thyroid cancers do not progress at an accelerated rate in the presence of TSI .
Either way, it may be in your best interest to attempt lifestyle changes which promote the reduction of these antibodies.;
When You Might Need Additional Tests
In these cases, doctors may choose to order a comprehensive panel of thyroid function tests to measure thyroxine such as Free T4, Total T4, Total T3, and thyroid antibodies, in addition to the TSH. A critical part of obtaining the best possible TSH test results and thyroid treatment involves ensuring youre receiving the right diagnostic tests.;
When Should I Get A Tsh Test
TSH is often the first test doctors order when they suspect a patient has a thyroid disorder. Both hypothyroidism and hyperthyroidism are common disorders. All patients with symptoms of these thyroid disorders should have their TSH checked.
If you are having symptoms of these disorders, your doctor may order a TSH or a thyroid panel test. Symptoms of hypothyroidism include:
- Rapid or irregular heartbeat
- Loose, frequent bowel movements
TSH is also used to evaluate patients who are suspected to have other thyroid disorders, such as goiter, thyroid nodule, thyroid cancer, Graves disease, or Hashimotos thyroiditis. These disorders can cause hypothyroidism or hyperthyroidism.
Screening with TSH for hypothyroidism in adults is controversial. Screening means testing in the absence of symptoms. It is most beneficial when early detection and treatment of disease helps people avoid subsequent medical problems. Some organizations, such as the American Association of Clinical Endocrinology, the American Thyroid Association, and the Endocrine Society, favor routine screening for thyroid problems in adults without symptoms.
Because thyroid disorders can complicate pregnancy, screening with a TSH test during pregnancy is recommended for some women. Pregnant women without symptoms of thyroid problems may be screened if they:
Controversy Over Optimal Tsh
While most laboratories define a normal TSH as between roughly 0.5 mU/l and 5.0 mU/l, some experts argue that the upper limit of a normal TSH should be loweraround 2.5 mU/l.
The reasoning behind this is that the vast majority of adults without thyroid disease have a TSH value between 0.45 and 4.12 mU/l.
In addition, some physicians believe older patients should have a TSH level that is greater than 4.0 mU/l or 5.0 mU/l, since TSH normally increases with age.
Doctors can avoid some of this controversy simply by looking at each person as an individual. For example, a person who still has significant symptoms of hypothyroidism at a TSH of 4.0 mU/l may do better with a goal TSH of around 1.0 mU/l.
In contrast, someone who has health riskssuch as heart disease or osteoporosismay benefit from having a goal TSH that is higher, perhaps around 5.0 mU/l or 6.0 mU/l.
In pregnancy, TSH should not be allowed to rise above 3.0 mU/l for the health of both the baby and mother.
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What Is A T3 Test
T3 TestsT3 tests measure triiodothyronine levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity hyperthyroidism.
In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 resulting in a lower proportion of T3.
T3 levels fall late in the course of hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.
Measurement of Free T3 is possible, but is often not reliable and therefore may not be helpful.
Patterns Of Thyroid Tests Associated With Thyroid Disease
Primary Hypothyroidism A high TSH and low thyroid hormone level can indicate primary hypothyroidism. Primary hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. Symptoms of hypothyroidism can include feeling cold, constipation, weight gain, slowed thinking, and decreased energy. Causes of primary hypothyroidism include:
- Autoimmune thyroid disease, including Hashimoto’s thyroiditis
- Thyroid gland dysfunction due to a medication
- Removal of all or part of the thyroid gland
- Radiation injury to the thyroid
- Excess treatment with anti-thyroid medications
Early or mild hypothyroidism may present as a persistently elevated TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.
It is important to remember that normal TSH levels in older individuals are higher than the normal ranges for younger individuals.
Primary Hyperthyroidism A low TSH and a high thyroid hormone level can indicate primary hyperthyroidism. Primary hyperthyroidism occurs when the thyroid gland makes or releases too much thyroid hormone. Symptoms of hyperthyroidism can include tremors, palpitations, restlessness, feeling too warm, frequent bowel movements, disrupted sleep, and unintentional weight loss. Causes of primary hyperthyroidism include:
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