TG (Thyroglobulin)

When a doctor recommends having Thyroglobulin (TG) levels checked, there are very specific reasons for those recommendations. This type of testing is fairly simple but essential to making sure there are no remaining thyroid cells after a thyroidectomy.

At YourDNA, we've compiled some helpful information about thyroglobulin so you can better understand why this test is performed and other important things you'll need to know.

What Is Thyroglobulin?

Thyroglobulin is a protein produced by the butterfly-shaped gland in the throat called the thyroid. This gland is important for regulating the way the body uses energy and is used in many body functions including:

• Breathing
• Heart rate
• Body weight
• Muscle strength
• Body temperatures
• Menstrual cycles

The thyroid is the only place in the body that produces thyroglobulin. When the thyroid gland is taken out of the body, thyroglobulin levels are tested to determine if there are any thyroid cells left in the body.

The TG or thyroglobulin gene is considered to be a protein-coding gene.

The Function of TG (Thyroglobulin)

TG and the thyroid are used as a place of storage for the iodine that many organs in the body need, including the stomach, salivary glands, breasts, cerebrospinal fluid, and thymus.

The presence of thyroglobulin antibodies could be an indication that there is some type of damage to the thyroid gland, usually caused by the immune system. A doctor may recommend having the Antithyroglobulin Antibody Test if they suspect a patient could be at risk of having an autoimmune disease such as Graves disease.

Around 15 to 20% of cancer patients ¹ have a presence of TG antibodies or TgAb in their bloodstream. When it comes to testing the levels of Tg, any TgAb in the bloodstream can interfere with the Thyroglobulin test, resulting in incorrect high or low values.

This can end up leading to complications because if a report states there's a low amount of Tg but it's false, there could be a delay in getting the patient the necessary help they need in a timely manner. A false report stating the levels are too high can end up causing the patient extra stress and anxiety and make them have additional scans that don't need to be performed.

Testing for Thyroglobulin

Individuals should get their thyroglobulin levels tested before and after they receive treatment for their thyroid cancer, including radioactive iodine therapy.

These levels are checked with a blood sample drawn from a vein in the arm. Depending on the laboratory, individuals might be asked to refrain from taking a multivitamin, or any supplement with high levels of vitamin B7 (Biotin) at least 12 hours before they take the test.

This is because B7 could lead to false results.

Since many thyroid disorders are genetic, there is genetic testing available to determine if you're a carrier of these conditions, such as hypothyroidism and congenital hypothyroidism. Some of the most common genetic testing performed includes:

Newborn Screening

Testing for Tg levels during a newborn screening is performed with a heel prick. Normal ranges of thyroglobulin in a newborn are around 17 and 160 micrograms/l. ²

Carrier Testing

Carrier screening is a genetic test and is a helpful way for individuals to determine if they carry the gene for a specific genetic disorder.

When individuals have this screening done before they conceive a child, it allows them to know what the chances are of having a child with a genetic condition.

Prenatal Testing

Prenatal testing is performed ³ with a blood test and the use of ultrasonography. This type of testing may be recommended if the fetus has any risk of having a genetic abnormality.

If there is a high risk of genetic issues, further prenatal testing may be done including an amniocentesis or chorionic villus sampling.

Why Is Thyroglobulin Tested?

The main reason why you'd want to get your thyroglobulin levels tested is to see how treatment for thyroid cancer is working and to see if there's a recurrence of thyroid cancer.

The purpose of thyroid cancer treatment is to get rid of all of the thyroid cells using surgery and radioiodine. This makes testing the levels is essential to monitoring the treatment.

After treatment, if the levels of thyroglobulin stay the same or there are extremely high thyroglobulin levels, there's a strong possibility that there are thyroid cancer cells left in the body. If the levels end up decreasing after treatment, this could mean there are no more thyroid cells left in the body, both regular and cancerous.

Chances are, after treatment, the doctor will want to check the thyroglobulin levels every few weeks starting right after the treatment ends to keep an eye on things. Testing eventually becomes less frequent.

Another reason why someone would get their levels tested is to find out the reason they have hypothyroidism or hyperthyroidism.

A normal range for thyroglobulin can vary depending on the blood lab used. At the Toronto General Hospital, a normal range would be 0 to 34 ug/L for those who still have their thyroid gland and 0-3 ug/L for those that have had the surgery to remove their thyroid or a thyroid ablation.

The reason why your thyroglobulin levels might come back abnormal could mean various things. Sometimes the levels can show decreased amounts after treatment, but then the levels start to rise again.

This could mean the cancer has returned after treatment. If little to no levels of thyroglobulin were found, this could indicate the cancer treatment worked.

The importance of measurement of thyroglobulin is to closely monitor how efficiently the cancer treatment is working for individuals with thyroid cancer.

Genetic Health Conditions Related to TG (Thyroglobulin)

Abnormal results from a thyroglobulin test could be an indication of a genetic health condition, some of which are autoimmune.

It's important to understand any symptoms that may occur as well as the available treatment options.

Graves Disease

Graves disease is a disorder of the immune system that occurs when there is too much of the thyroid hormone being produced. Typical symptoms of this include:

• Frequent bowel movements
• Anxiety
• Change in menstrual cycles
• Bulging eyes
• Fatigue
• Heart palpitations
• Enlarged thyroid gland
• Heat sensitivity
• Weight loss
• Thick skin, reddish in color
• Reduced libido
• Erectile dysfunction

This condition is believed to be caused by environmental and genetic factors ⁴, but the exact cause is unknown at this time. When someone has Graves disease, their immune system makes an abnormal antibody that imitates the function of the normal hormone that stimulates the thyroid.

It's believed that people affected by Graves disease carry the gene for the disease, possibly leading them to pass it on to their offspring.

Some of the most common treatment options for Graves disease include:

• Antithyroid medications such as propylthiouracil (PTU)
• Radioactive iodine or RAI
• Surgery to remove all or some of the thyroid gland

Surgery may be recommended if the patient is pregnant or if they cannot take antithyroid medication.

Congenital Hypothyroidism

Congenital hypothyroidism is when there is not enough of the thyroid hormone being produced in newborn infants.

There are numerous possible causes of this condition, some of which are genetic. The diet of the mother during pregnancy ⁵ is also another factor that can lead to congenital hypothyroidism. Symptoms include:

• Large, thick tongue
• Puffy face
• Jaundice
• Hoarse cry
• Constipation
• Distended stomach
• Poor muscle tone

Treatment of this condition involves restoring the thyroid hormone levels to normal, such as with a synthetic version of the hormone called levothyroxine.

Hashimoto Thyroiditis

Hashimoto thyroiditis is when the thyroid is attacked by the immune system, often leading to a thyroid gland that isn't as active as it should be. Hormone replacement therapy is the most common treatment for this condition.

An antithyroglobulin antibody test measures the antibodies to thyroglobulin, which can be helpful in determining Hashimoto thyroiditis and other conditions. The symptoms associated with Hashimoto thyroiditis are:

• Muscle weakness
• Constipation
• Fatigue
• Puffy face
• Increased sensitivity to cold
• Weight gain
• Depression
• Memory lapses
• Muscle aches
• Prolonged menstrual bleeding
• Brittle nails

In most cases of this condition, the cases are sporadic, and occur when there isn't a family history of it. Then Hashimoto thyroiditis is inherited, it follows an autosomal recessive inheritance pattern, where the parents carry one copy of the condition, but they do not have any signs and symptoms.

Subacute Thyroiditis

Subacute thyroiditis is an acute inflammatory disease of the thyroid. This condition is likely caused by a virus in the thyroid gland. It is not known for sure if subacute thyroiditis is genetic, but it does seem to occur more within families.

Some of the most common symptoms associated with this condition include:

• Fever
• Weakness
• Hoarseness
• Fatigue

There are several types of treatment options available, some of which include over-the-counter anti-inflammatory medications like ibuprofen, beta blockers, and corticosteroids. Treatment options are typically on a temporary basis and are determined by the severity of the symptoms.

Thyroid Dyshormonogenesis 3

Thyroid Dyshormonogenesis 3 is a condition that causes a permanent thyroid deficiency, typically present at birth. This condition is caused by hereditary defects and the absence of dehalogenase enzymes.

Individuals with this condition generally develop hypothyroidism, which is an underactive thyroid.

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