What is thyroid hormone? | What’s included in a thyroid panel? | Normal thyroid levels | Thyroid test results chart | Other types of tests | Next steps
Your healthcare provider may recommend a thyroid panel test to determine if you have a thyroid condition. The thyroid is a butterfly-shaped gland in the neck. It produces hormones that regulate metabolism. When these hormones are out of balance, it can cause myriad health problems, including unexpected weight loss and fertility problems. The good news is most thyroid diseases are treatable.
But thyroid testing can be confusing. Here, learn the different types of thyroid tests and what your results mean.
What is thyroid hormone?
Your thyroid gland uses iodine from the food you eat to produce two hormones: triiodothyronine (T3) and thyroxine (T4). “Your appetite, gut motility, and even absorption of substances are all affected by thyroid gland hormones,” says Carrie Lam, MD, cofounder and medical director of Lam Clinic in Tustin, California. Thyroid hormones aid in digestion, cardiovascular health, brain development, and growth in young people.
Two regions of the brain help to regulate how much of these hormones the thyroid produces: the hypothalamus and pituitary gland. The hypothalamus releases thyrotropin-releasing hormone (TRH), which prompts the pituitary gland to release thyroid-stimulating hormone (TSH).
When T3 and T4 are too low in the body, the hypothalamus and pituitary gland produce more TRH and TSH. TSH then prompts the thyroid to put out more T3 and T4. When levels are too high, they secrete less TRH and TSH. It’s important to have normal thyroid levels since an imbalance could throw off metabolic processes in other areas of the body.
What’s included in a thyroid panel?
If your healthcare provider is unsure what has gone awry with your thyroid, a full thyroid panel can help point toward what’s causing your symptoms. It is a simple blood test. You don’t need to do anything to prepare. Typically, it involves testing:
- TSH: The most basic test, this measures if your body is prompting your thyroid to produce hormones correctly. When it’s too low, it can indicate hypothyroidism; too high can mean hyperthyroidism.
- Free T4 (fT4): Your body converts this hormone into T3 before it can use it. Its primary job is to help transport T3 through your body. This test measures how much of this hormone is in your body. When fT4 is too low, it can indicate hypothyroidism; too high can mean hyperthyroidism. Free T4 is usually preferred as compared to Total T4. It’s more accurate to show active T4 levels.
- Total T4: Measures all thyroxine in your body. When total T4 is too low, it can indicate hypothyroidism; too high can mean hyperthyroidism. Total T4 is normally tested in pregnant patients.
- Free T3 (fT3): This is the active form of thyroid hormone that can be used by your organs, such as the liver. This test measures how much unbound T3 is in your body. Too low fT3 can indicate hypothyroidism; too high can mean hyperthyroidism. Free T3 test assays are considered unreliable, and may be omitted from your test. If T3 needs to be checked, Total T3 is has higher accuracy.
- Total T3: Measures all T3 in your body, even that which is unusable because it’s already bound to a protein.
- TPO antibodies: This test measures thyroid peroxidase (TPO). High levels can indicate Hashimoto’s thyroiditis, an autoimmune condition.
- ReverseT3 (rT3): This is an inactive form of T3, produced when T4 is metabolized. When rT3 levels are too high or too low, it can indicate trauma, inflammation after surgery, or malnutrition.
If you’ve already been diagnosed with a thyroid condition, typically testing is more specific. “Most endocrinologists are targeted with what they order, rather than sending a general thyroid panel,” explains Aleem Kanji, MD, a board-certified endocrinologist with Ethos Endocrinology in Houston, Texas. “The specific labs chosen are based on the person’s diagnosis, treatment, and/or required monitoring.”
Normal thyroid levels
There are several factors that can affect thyroid function tests including:
- Age: As you get older, the higher chances you have of fluctuations in thyroid levels.
- Sex: Women tend to have more thyroid hormone imbalances, including both hypothyroidism and hyperthyroidism, than men.
- Pregnancy: A low TSH level early in pregnancy can be expected, according to the American Thyroid Association. Oftentimes, providers won’t treat low TSH levels in pregnant women. However, TSH shouldn’t rise above a certain number depending on your trimester. High TSH levels could affect your and your baby’s health.
- Medications: Certain medications can affect how thyroid hormone is absorbed and used in the body, particularly glucocorticoids, furosemide, phenytoin, amphetamines, and estrogen. Taking estrogen for hormone imbalances can increase thyroxine-binding globulin (TBG), which is a protein that binds to thyroid hormones in the blood. When TBG levels are higher than they should be, more thyroid hormones are binded and there is less free thyroid hormone circulating in the blood. “This is particularly relevant in women with hypothyroidism taking thyroid medication,” Dr. Kanji says. “They may require an increased dose of their thyroid hormone after starting estrogen therapy.”
- Supplements: High doses of biotin, a B-vitamin supplement, can cause falsely low levels of TSH and a high T3 and T4 which together can indicate hyperthyroidism. “In other words, the results would look exactly as if a person is hyperthyroid, when in fact the levels could be normal,” Dr. Kanji explains.
Below is a thyroid test results chart of different ranges, but it’s important to note that different laboratories have different reference ranges and a person’s age and comorbidities can determine the correct range for each person to be normal or abnormal. Talk with your provider to find out your own test results and what they mean.
Thyroid test results chart |
||
|---|---|---|
| Test | Result | Meaning |
| TSH | <0.1 milliunits per liter (mU/L) | Overactive thyroid problem that’s symptomatic |
| 0.1-0.5 mU/L | Subclinical overactive thyroid problem | |
| 0.4-4.5 mU/L | Normal range | |
| 4.7-10 mU/L | Subclinical hypothyroidism | |
| >10 mU/L | Low thyroid problem that’s symptomatic | |
| Total T3 | <100-200 nanograms per deciliter (ng/dL) | Lower than normal levels, can indicate hypothyroidism |
| 100-200 ng/dL | Normal range | |
| >200 ng/dL | Higher than normal levels, can indicate hyperthyroidism | |
| Free T3 (fT3) | <130 picograms per deciliter (pg/dL) or 2.0 picomoles per liter (pmol/L) | Lower than normal levels, can indicate hypothyroidism |
| 130-450 pg/dL, or 2.0 to 7.0 pmol/L | Normal range | |
| >450 pg/dL, or 7.0 pmol/L | Higher than normal levels, can indicate hyperthyroidism | |
| Total T4 | <5.0 ug/dL (micrograms per deciliter of blood) | Lower than normal levels, can indicate hypothyroidism |
| 5.0-12.0 ug/dL | Normal range | |
| >12 ug/dL | Higher than normal levels, can indicate hyperthyroidism | |
| Free T4 (fT4) | <0.9 ng/dL or 12 pmol/L | Lower than normal levels, can indicate hypothyroidism |
| 0.9 – 1.8 ng/dL or 12 to 30 pmol/L | Normal range | |
| >1.8 ng/dL or 30 pmol/L | Higher than normal levels, can indicate hyperthyroidism | |
| TPO antibodies (TPOAb) | Negative | Normal, no antibodies found, symptoms probably aren’t caused by autoimmune disease |
| Positive | Indicates autoimmune disease | |
| Reverse (rT3) | <10 ng/dL | Can indicate hypothyroidism |
| 10-24 ng/dL | Normal range | |
| >24 ng/dL | Can occur in people who are critically ill |
Sources:
- T3, T4, TSH, Endocrine Web
- T3, MedlinePlus
- T3, Mount Sinai
- Free T4, UCSF
- Thyroid antibodies, MedlinePlus
- TPO, Mayo Clinic Laboratories
- RT3, Mayo Clinic Laboratories
TSH test results
Normal TSH levels in adults are usually 0.4-4.5 milliunits per liter (mU/L). Higher or lower levels could indicate a thyroid disorder.
Elevated TSH can indicate hypothyroidism. “A high TSH typically occurs when thyroid hormone levels in the blood are low,” Dr. Kanji explains. “In other words, the brain is detecting a low level of thyroid hormone, and in response, increases the TSH level to stimulate the thyroid gland to produce more thyroid hormone.”
On the other hand, low TSH indicates thyroid hormone levels in your blood are too high. This means “the brain is detecting a high level of thyroid hormone, and in response, decreases the TSH level to stop the thyroid gland from producing more thyroid hormone,” Dr. Kanji says. This could mean you have hyperthyroidism.
T3 and T4 test results
If your TSH levels are off, your provider will most likely check your T4 levels and T3 levels. If one or both of these come back elevated, along with a low TSH, it usually indicates hyperthyroidism. If they are low, it can indicate hypothyroidism. Further testing would be necessary to find the cause.
TPO antibodies results
Thyroid peroxidase (TPO) antibodies are antibodies that end up attacking your thyroid gland instead of the viruses and bacteria they’re supposed to target. If thyroid antibodies are present, it can mean you might have a thyroid condition that’s autoimmune-related.
If your test result comes back negative it means there were no antibodies present in the sample and that your thyroid condition probably isn’t related to an autoimmune condition. If your results are positive, it can indicate you might have a thyroid condition caused by an autoimmune disease, or that you have the potential to develop a future thyroid condition. High levels of TPO antibodies could mean you have an increased chance of having a miscarriage, preeclampsia, or premature birth.
Other types of thyroid tests
Your provider may also perform a physical exam of the thyroid by feeling your next. According to Dr. Kanji, this might be looking at the front of your neck and from behind you to see if there are any concerns such as an enlarged thyroid gland or nodules. If there is swelling, your provider will want to determine if it’s present on one or both sides of the neck.
If a physical exam shows concerning symptoms, a thyroid ultrasound can confirm if nodules or goiter is present. Goiter can also be the result of thyroid tumors, which are typically benign. It uses high-frequency sound waves to make an image of the thyroid, and can help diagnose signs of thyroid cancer.
Next steps: What if I’m diagnosed with a thyroid condition?
The only way to tell if you have a thyroid disease is to be seen by your provider for an exam or blood testing. Your primary care provider may feel comfortable ordering thyroid tests and managing medications, but some will refer patients to an endocrinologist instead. Here are the common thyroid conditions you might be diagnosed with and how they’re typically treated.
Hypothyroidism
The most common thyroid condition is hypothyroidism, or underactive thyroid. This means the thyroid doesn’t make enough thyroid hormone to ensure proper metabolism regulation. “The result of this is that it’s very easy to gain weight,” Dr. Lam says.
There are different causes of hypothyroidism, the most common being Hashimoto’s thyroiditis. Another cause, though rarer, is abnormal pituitary gland growth. This results in an excess of TSH.
Symptoms of hypothyroidism include:
- Weight gain
- Fatigue
- Dry, brittle nails
- Itching
- Constipation
- Irregular menstrual cycles
- Cold sensitivity
The treatment for hypothyroidism is usually a medication called Synthroid (levothyroxine). You may spend a few months adjusting your dose in order to balance thyroid hormone. It’s important to take the medication on an empty stomach in the morning and avoid missing doses.
Hyperthyroidism
If you have hyperthyroidism, your thyroid is making too much thyroid hormone. The most common cause of hyperthyroidism is Graves’ disease. A second, less common, cause of low TSH is when the pituitary gland isn’t functioning as it should, and makes too little TSH, known as central hypothyroidism.
Dr. Lam explains the most noticeable symptom of Grave’s disease is swelling behind your eyes. “Hyperthyroidism may also result from thyroid nodules, which are small lumps that develop inside the thyroid gland,” Dr. Lam says. These lumps may actually produce their own thyroid hormones.
Other symptoms of hyperthyroidism include:
- Fast or irregular heart rate
- Anxiety
- Shaking
- Weight loss
- Weakness of the muscles
- Unable to tolerate warm temperatures, and/or sweating
- Diarrhea
Medications are one way to treat hyperthyroidism. Tapazole (methimazole) is commonly prescribed to slow down the production of thyroid hormone. It can take a few months in order for your hormone levels to level out and become normal. Radioactive iodine treats thyroid dysfunction is caused by too much thyroid hormone being produced. It works by getting inside the thyroid cells and killing them.
In rare cases, surgery may be necessary to remove a portion of the thyroid gland. This usually means you will then develop hypothyroidism and would be on thyroid hormone replacement therapy for the rest of your life.
RELATED: Hypothyroidism vs. hyperthyroidism
Bottom line—thyroid disease is treatable
It’s important to know that thyroid disease is common and very manageable with the right treatment regimen. In addition to the treatments listed above, diet, supplements, and healthy lifestyle changes can help support thyroid health. However, if thyroid problems are left untreated, complications can be serious. People with untreated thyroid disease are at a higher risk of medical conditions like heart disease, osteoporosis, and stroke. If you have a family history of thyroid disease or if you’re presenting symptoms, visit your healthcare provider for a thyroid panel test.
