How Thyroid Function Is Tested
Thyroid tests use blood or urine to measure thyroid health. Some tests use both.
A blood or urine thyroid test may measure:
- TSH - Thyroid Stimulating Hormone
- fT4 - Free levels of thyroxine (T4)
- ft3 - Free levels of triiodothyronine (T3)
- TG - Thyroglobulin
- TPOab - Antibody to thyroid peroxidase
What Does "Free Levels" Mean?
Free levels of hormones refers to the amount of the hormone that is not bound to proteins and is therefore available for use by the body. Tests should specify whether they measure total, free or both.
What Is TSH?
The pituitary gland, a pea-sized gland located at the base of the brain, creates TSH to regulate the thyroid's production of hormones.
What Is T4?
T4 is one of the two major hormones created by the thyroid gland. It is a precursor to T3. This means that T3 derives from T4.
What Is T3?
T3 is the second main thyroid hormone. It is created in small amounts by the thyroid. The balance of T3 found in the body is synthesized from T4.
Both T4 and T3 can become bound by proteins and therefore inactive unless they are released by the proteins through signaling. Faulty signaling or excessive levels of binding proteins are common roots of disorders. This is a reason some tests focus on free levels.
What Is Thyroglobulin?
Thyroglobulin is a protein made by thyroid cells. It that binds to the mineral iodine to form the building blocks of T3 and T4. Iodine deficiency can cause Tg to accumulate, thus high levels of protein may indicate iodine deficiency A Tg test is also used as a "tumor marker" to measure the success of thyroid cancer treatment. The goal of thyroid cancer treatment is to destroy all thyroid hormones. If Tg is detect in blood post-cancer treatment, it may mean the cancer is still present.
What are Thyroid Antibodies?
The adaptive immune system creates antibodies specific to each attack on the body. Identifying the presence of, the type and their levels offers insight into what immune system threat an individual is facing and the extent of the attack.
Thyroid tests may look for the presence of antibodies. If they are found, the test will also identify their type.
What Does Positive TPOab Mean?
Although there are several types of thyroid antibodies, the presence and level of TPOAb is the focus of a thyroid function test. Positive TPOAb shows that the body has developed antibodies against healthy thyroid cells. It is an autoimmune response.
Positive TPOAb means that your test has showed levels outside of the normal range. It may be a sign of the genetic disorder Hashimoto's thyroiditis (hypothyroidism), one of the most common Autoimmune Thyroid Diseases (AITDs). However, TPOAb presence does not automatically mean you have thyroid disease. The amount needs to be analyzed along with other aspects of your thyroid and overall health.
What Is The Normal Range For TPOAb?
The normal adult reference range for TPOAb is less than 70 IU/mL. It is important to note that there is discrepancy in the medical industry on what is the normal reference range for TPOAb. Your lab test results will provide a reference range and your doctor will discuss your results with you.
Autoimmunity can be temporary or chronic. In fact, women are susceptible to transient AITD, particularly caused by elevated TPOab levels during pregnancy.1 The link has demonstrated higher risk for pregnancy complications.1
Studies show age, gender, TSH serum levels can also influence TPOab.2 Additionally, smoking has been tied to above normal TPOab.3
Chronic autoimmune diseases can debilitate individual or multiple parts of the body. Arthritis, lupus and AIDS are examples. Cytokine storms, an extreme autoimmune response, is a leading cause of COVID-19 fatalities. Cytokine storms can engulf the body and cause multiple organ failure (sepsis). The most severe stage of sepsis is septic shock which can lead to death.
What Does The Thyroid Do?
The thyroid is a small butterfly shaped gland located at the base of the neck. It is part of the endocrine system. It creates three hormones.
- Thyroxine (T4)
- Triiodothyronine (T3)
T3 and T4 regulate Basal Metabolic Rate (BMR), which is the creation of energy from food. Energy is measured in calories and energy maintains life!
Basal metabolic rate is not the same as metabolism. Metabolism refers to all chemical processes in the body that support life. Basal metabolic rate only involves calories.
Thyroid disorder, or inadequate basal metabolic rate, has a major negative impact on the heart, liver, brain and temperature regulation.
What Is Calcitonin?
Calcitonin regulates the use of calcium.
What Are The Different Types Of Thyroid Disorders?
- Thyroid cancer
- Thyroid nodules - lumps in the thyroid gland
- Thyroiditis - swelling of the thyroid
- Goiter, a type of thyroiditis
The most common thyroid diseases are Graves' Disease (hyperthyroidism) and the genetic disorder Hashimoto's thyroiditis (hypothyroidism). Both are autoimmune diseases.
Thyroid cancer, pituitary gland disorders, hyperthyroidism or hypothyroidism may also inflame the thyroid, resulting in thyroiditis.
Hashimoto Disease develops when the immune system attacks the thyroid gland and inhibits its production of T4 and T3. With Graves' Disease, the immune system sends out antibodies that imitate TSH and trick the pituitary gland to overproduce T4.
Goiter may or may not be malignant. Iodine, a natural mineral that the body cannot make, is essential for the creation of thyroid hormones. Iodine deficiency is the leading cause of goiter in the world. 5
Iodine is present in many foods including
- Fish (such as cod and tuna), seaweed, shrimp
- Dairy products (such as milk, yogurt, and cheese)
- Products made from grains (like breads and cereals)
- Certain fruits and vegetables like prunes, cabbage, and broccoli
- Some fruits and vegetables are grown in iodine rich soil and therefore fortified with iodine
- Iodized salt
In mild cases, adding iodine to the diet can stave off or reduce goiter.
|US RDA Iodine
|Birth to 6 months||110 mcg|
|Infants 7–12 months||130 mcg|
|Children 1–8 years||90 mcg|
|Children 9–13 years||120 mcg|
|Teens 14–18 years||150 mcg|
|Pregnant teens and women||220 mcg|
|Breastfeeding teens and women||290 mcg|
Is There A Cure For Thyroid Disease?
Thyroid disease tends to be chronic but can be well-managed with prescription medications and or/diet and lifestyle changes.
Thyroid Replacement Therapy, adds hormones extracted from desiccated porcine (pig) thyroid or lab-made replicas of human thyroid hormones. Treatment goals may be suppressive, in the case of hyperthyroidism, or augmentative for hypothyroidism. Directly adding T4 and/or T3 to the body, depending on administration, can work either way.
In the case of thyroid cancer, nodules or other abnormalities, surgery (partial or total removal of the thyroid) may be required for biopsy or to remove malignant tissue. A goiter that is benign but disrupting breathing or is bothersome for other reasons, may also require surgery.
How Do I Know If I Have Thyroid Problems?
To verify thyroid dysfunction, you need a thyroid test. However, when your thyroid is not working properly, you'll probably get plenty of warning. Unfortunately, the symptoms are easily confused with any number of problems include hormonal imbalance, diabetes, liver conditions and poor diet, particularly, iodine deficiency. Transient thyroid disorders may occur during pregnancy and due to prolonged periods of high stress.
Learn more about thyroid disease, symptoms and treatments.
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1 Bhattacharyya R, Mukherjee K, Das A, Biswas MR, Basunia SR, Mukherjee A. Anti-thyroid peroxidase antibody positivity during early pregnancy is associated with pregnancy complications and maternal morbidity in later life. J Nat Sci Biol Med. 2015;6(2):402-405. doi:10.4103/0976-9668.160021
2 Amouzegar A, Gharibzadeh S, Kazemian E, Mehran L, Tohidi M, Azizi F. The Prevalence, Incidence and Natural Course of Positive Antithyroperoxidase Antibodies in a Population-Based Study: Tehran Thyroid Study. PLoS One. 2017;12(1):e0169283. Published 2017 Jan 4. doi:10.1371/journal.pone.0169283
3 Gu XL, Mao JY, Shan ZY, et al. Zhonghua Liu Xing Bing Xue Za Zhi. 2007;28(1):53-56.
4Romani, L., Tomino, C., Puccetti, P. et al. Off-label therapy targeting pathogenic inflammation in COVID-19. Cell Death Discov. 6, 49 (2020). https://doi.org/10.1038/s41420-020-0283-2
5 Ahad F, Ganie SA. Iodine, Iodine metabolism and Iodine deficiency disorders revisited. Indian J Endocrinol Metab. 2010;14(1):13-17.
6 Office of Dietary Supplements - Iodine. Ods.od.nih.gov. https://ods.od.nih.gov/factsheets/Iodine-Consumer/#h2. Published 2020. Accessed July 24, 2020.