Underactive Thyroid/ Overactive Thyroid /TBG Test

TBG Blood Test (Thyroxine-Binding Globulin) is a kind of test to measure the level of a protein that moves in the bloodstream for thyroid hormone disorders and this protein is called thyroxine-binding globulin (TBG). The normal range is 13 to 39 micrograms per deciliter (µg/dL), or 150 to 360 nanomoles per liter (nmol/L). Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. In cases of high TBG, more thyroid hormone will be bound, decreasing free hormone in the blood. This will lead to an increase in TSH, and more thyroid hormones will be produced.

A hormone that is made by the thyroid gland and contains iodine. Thyroxin increases the rate of chemical reactions in cells and helps control growth and development. Thyroxin can also be made in the laboratory and is used to treat thyroid disorders.

How the Test is Performed

A blood sample is taken and then sent to a laboratory for testing. Special tests called electrophoresis or radioimmunoassay are used to measure the TBG level in your blood.

How to Prepare for the Test

Certain drugs and medicines can affect test results. Your health care provider may tell you to stop taking a certain medicine for a short time before the test. Never stop taking any medicine without first talking to your provider.

These medicines and drugs can increase TBG levels:

  • Estrogens, found in birth control pills and estrogen replacement therapy
  • Heroin
  • Methadone
  • Phenothiazines (certain antipsychotic drugs)

The following medicines can decrease TBG levels:

  • Depakote or depakene (also called valproic acid)
  • Dilantin (also called phenytoin)
  • High doses of salicylates, including aspirin
  • Male hormones, including androgens and testosterone
  • Prednisone

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

This test may be done to diagnose problems with your thyroid.

Normal Results

If electrophoresis is used, normal values may range from 10 milligrams per 100 milliliters (10 mg/100 mL) to 24 mg/100 mL.

If radioimmunoassay is used, a normal range is 1.3 to 2.0 mg/100 mL.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

An increased TBG level may be due to:

  • Acute intermittent porphyria (a rare metabolic disorder)
  • Hypothyroidism (underactive thyroid)
  • Liver disease
  • Pregnancy (TBG levels normally increased during pregnancy)

Note: TBG levels are normally high in newborns.

Decreased TBG levels may be due to:

  • Acute illness
  • Acromegaly (a disorder caused by too much growth hormone)
  • Hyperthyroidism (overactive thyroid)
  • Malnutrition
  • Nephrotic syndrome (symptoms that show kidney damage is present)
  • Stress from surgery

Risks

Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks of having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood buildup under the skin)
  • Infection (a slight risk any time the skin is broken)

FAQ

What does TBG test for?

  • The TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine-binding globulin (TBG).

Why is TBG increased in hypothyroidism?

  • Increased TBG levels may be due to hypothyroidism, liver disease, and pregnancy. In cases of high TBG, more thyroid hormone will be bound, decreasing free hormone in the blood.
  • This will lead to an increase in TSH, and more thyroid hormones will be produced.

What is a normal TBG level?

  • The normal range is 13 to 39 micrograms per deciliter (µg/dL), or 150 to 360 nanomoles per liter (nmol/L).
  • Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.

Can you measure TBG?

  • The serum TBG level test measures the amount of TBG in your blood. This can help doctors assess thyroid problems. TBG deficiency usually accompanies an underlying illness. A low TBG level doesn’t cause symptoms.

What is high thyroxine-binding globulin?

  • Thyroxine binding globulin (TBG) is the high-affinity serum binding protein for thyroxine and triiodothyronine.
  • Normally, the thyroid adjusts to changing concentrations of TBG by producing more, or less, a thyroid hormone to maintain a constant level of metabolically important free hormone.

Is thyroxine-binding globulin the same as thyroglobulin?

  • Thyroglobulin is the protein produced in the thyroid follicles and takes part in thyroxine formation. Thyroxine binding globulins are the protein that binds to thyroxine.

What is the role of thyroxine-binding globulin?

  • Thyroxine-binding globulin is a protein that carries hormones made or used by the thyroid gland, which is a butterfly-shaped tissue in the lower neck.
  • Thyroid hormones play an important role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism).

What happens if thyroglobulin is high?

  • Very high levels of thyroglobulin may suggest metastatic or recurrent disease. About one-fourth of patients who have thyroid cancer have antibodies to thyroglobulin.
  • Antibodies should be checked along with thyroglobulin because if they are present, they could interfere with the measurement of thyroglobulin.

What happens if the thyroglobulin antibody is high?

  • If you have high levels of antithyroglobulin antibodies in your blood, it may be a sign of a serious autoimmune disorder, such as Graves’ disease or Hashimoto’s thyroiditis.
  • In some cases, you may have antithyroglobulin antibodies in your blood without any specific complications.

What is the meaning of thyroxine?

  • (thy-ROK-sin) A hormone that is made by the thyroid gland and contains iodine. Thyroxin increases the rate of chemical reactions in cells and helps control growth and development. Thyroxin can also be made in the laboratory and is used to treat thyroid disorders.

What causes an increase in thyroglobulin?

  • Levels in the blood are directly proportional to the size of the thyroid. For example, thyroid cancer cells enlarge the gland and make thyroglobulin in high amounts. In fact, any disorder that increases the size of the thyroid (cancer, autoimmune disease, nodules, etc.) can raise thyroglobulin levels.

How can I lower my thyroglobulin levels?

Beneficial supplements include:
  • Selenium. Studies show that taking 200 mcg of selenium per day may help reduce antithyroid peroxidase (TPO) antibodies and improve well-being in people with Hashimoto’s thyroiditis.
  • Zinc.
  • Curcumin.
  • Vitamin D.
  • B complex vitamins.
  • Magnesium.
  • Iron.

What is the side effect of thyroxine?

  • Tell your doctor if you have any of the following symptoms while you are taking levothyroxine: chest pain, rapid or irregular heartbeat or pulse, uncontrollable shaking of a part of the body, nervousness, anxiety, irritability, difficulty falling asleep or staying asleep, shortness of breath, or excessive sweating.

Where does thyroxine come from?

  • Thyroxine is a hormone made in the thyroid gland that controls this metabolic rate, i.e. it keeps the body functioning at the right speed.

Is thyroglobulin the same as TSH?

  • Since thyroid-stimulating hormone (TSH) stimulates thyroid follicular cells to produce thyroglobulin, serum thyroglobulin concentrations will be higher in patients with a raised TSH if there is remaining thyroid tissue or in the presence of a recurrent tumor.

Can thyroid antibodies return to normal?

  • In patients with autoimmune hypothyroidism (Hashimoto’s thyroiditis), TPO antibodies usually remain in the body.
  • Levels may reduce over time, but hardly ever normalize completely, even after the medication has restored thyroid levels to normal.

What foods should I avoid when taking levothyroxine?

  • levothyroxine food
  • In addition, absorption of levothyroxine may be decreased by foods such as soybean flour, cottonseed meal, walnuts, dietary fiber, calcium, and calcium-fortified juices.
  • These foods should be avoided within several hours of dosing if possible.

What does thyroglobulin of 0.1 mean?

  • The investigators found that when the basal thyroglobulin level under thyroid hormone suppression therapy is <0.1 ng/ml, it accurately predicts that the stimulated thyroglobulin level will be <1, which indicates the absence of residual cancer cells.

Does thyroxine reduce thyroid antibodies?

  • The present study showed that levothyroxine treatment significantly decreased the TPOAb and TgAb levels of the hypothyroid patients.
  • These results are also supported by some previous studies. Levothyroxine treatment significantly reduced the TPOAb levels in both hypothyroid and euthyroid patients with AIT.