Laboratory Tests and Thyroid Diseases

Guide to the Thyroid and Thyroid Diseases

Your thyroid is a small butterfly-shaped gland on the base of your throat. The thyroid plays an essential role in helping to control the metabolism of your body by producing thyroid hormones, mainly triiodothyronine (T3) and thyroxine (T4). They are substances that travel through your blood to all parts of your body. Thyroid hormones inform the cells within your body how quickly to produce proteins and use energy. Calcitonin is also made by the thyroid gland. Calcitonin is a hormone that helps with regulating the levels of calcium inside the blood through inhibiting re-absorption (breakdown) of bone as well as increasing the elimination of calcium through the kidneys.     

The body features an elaborate feedback system for controlling the amounts of T3 and T4 inside the blood. Whenever the blood levels of these hormones fall, thyrotropin-releasing hormone is released by the hypothalamus. This, in turn, causes thyroid-stimulating hormone (TSH) to be released by the pituitary gland. The thyroid gland is stimulated by TSH to secrete and produce T3 and T4 (primarily). Whenever the system is functioning correctly, thyroid production turns off and on to maintain thyroid hormone levels that are relatively stable. 

Inside of the thyroid, a majority of the T4 is bound to the thyroglobulin protein and stored away. Whenever necessary, more T4 is produced by the thyroid gland and/or some of the stored amount is released. Inside the blood, most of the T3 and T4 are bound to thyroxine-binding globulin (TBG) protein and are inactive. There are small, unbound amounts, called free T3 and free T4, that are the active forms of these hormones. T4 gets converted into T3 inside of the liver as well as other tissues. The primary responsibility of T3 is to control body function rates.

Thyroid diseases are mainly conditions affecting how much thyroid hormones are produced. The American Thyroid Association estimates that there are 20 million Americans who some type of thyroid disease, and around 60% of people with thyroid disease are not aware of it. It is more likely for women to have thyroid issues than men, with 1 out of 8 women developing a thyroid disorder at some point in her life. Below is a list of the most common types of thyroid disorders.

Types of Abnormal Thyroid Functioning

Some of the diseases of abnormal thyroid functioning include the following:

Hypothyroidism: this refers to a condition where there is an insufficient amount of thyroid hormone and body functions slow down. Some of the main symptoms include menstrual irregularity within women, fatigue, hair loss, puffy skin, cold intolerance, constipation, dry skin, and weight gain. Myxedema, which is severe untreated hypothyroidism, may lead to coma, seizures, and heart failure. In children, hypothyroidism may delay sexual development and stunt growth. Specific hypothyroidism types include the following: 

Congenital hypothyroidism: a condition that affects babies from birth caused by insufficient thyroid hormone; is mainly due to when a thyroid gland is partially developed, missing, or when it is in part of the body that is abnormal. The remainder of cases is either due to an enlarged or normal-sized thyroid that isn’t functioning correctly or producing enough thyroid hormone. When this condition is left untreated, it may cause delays in intellectual and physical development. In the US, hypothyroidism testing is done as part of blood screening programs for newborns because early detection, as well as treatment, helps to minimize long-term damage to babies. 

Hashimoto thyroiditis: in the US, this is the most common type of hypothyroidism. It is a chronic autoimmune condition where the thyroid is targeted by the immune system, which causes damage and inflammation and produces autoantibodies. With Hashimoto thyroiditis, thyroid hormones are produced in lower quantities.

Iodine deficiency: when the element of iodide is lacking in the body, it diminishes the thyroid gland’s ability to produce enough thyroid hormone. There are three iodides in T3 and four iodides in T4. Throughout the environment, iodine is present. However, most iodine is contained in seaweed and seawater. Individuals who reside in countries with limited access to the ocean frequently suffer from iodine deficiency unless they consume food supplemented with iodine. Iodide is fortunately used for fighting bacterial growth in various foods (like iodized salt) and many dietary supplements as well.

Hyperthyroidism: excessive thyroid hormone, also referred to as “overactive thyroid.” Body functions are accelerated, and symptoms include weakness, tremors within the hands, difficulty sleeping, weight loss, anxiety, increased heart rate, and diarrhea sometimes. There might be puffiness surrounding the eyes, irritation, dryness, and bulging eyes in some cases. The person who is affected might experience visual disturbances and light sensitivity. Since the eyes might not move in a normal way, the individual might look like they are staring. 

Specific kinds of hyperthyroidism include the following:

Graves disease: this is the most common cause of hyperthyroidism. This is a chronic autoimmune disorder where the immune system of the affected individual produces antibodies that act like TSH, which stimulates the thyroid to make excessive thyroid hormone amounts.

Thyroid tumor: a small benign tumor might become insensitive to low TSH negative feedback and continuing producing thyroid hormone in excessive amounts.

Abnormal thyroid stimulation: when there is a tumor in the cells producing TSH, it may result in the excessive production of thyroid hormone. The hormone called human chorionic gonadotropin (hCG), which supports fetus growth during pregnancy, can act like TSH and produce hyperthyroidism in pregnant women if they have very high hCG levels.

Goiter: a visible enlargement of the thyroid gland. This condition in the past was common and caused by an iodine deficiency. However, now that food is supplemented with iodine, there are significantly fewer dietary-related goiter incidents in the US. However, in other regions of the world, iodine-related goiters are common still and in some countries are the most common cause of hypothyroidism. Goiters can compress critical structures within the neck, which include the esophagus and trachea. That compression can make it hard to swallow and breathe. Goiters can be caused by any diseases that are listed above. Thyroid hormone resistance syndrome is a rare cause and a mutation within the thyroid hormone receptor that reduces the functioning of the thyroid hormone.

Thyroiditis: an inflamed thyroid gland; it can be associated with either hyper- or hypothyroidism. It can be quite painful and feel like a sore throat, and it can also be painless. Thyroiditis can be caused by several things such as exposure to toxic chemicals, infection, or autoimmune disorders (especially if you have Hashimoto thyroiditis). The cause of thyroiditis can also be unknown. Depending on what the cause is, it may be chronic, transient, or acute.

Diseases that may be presented as thyroid tumors include the following:

Thyroid nodule: this is a small lump located on a thyroid gland. It can be either a fluid-filled or solid cyst. The nodules are very common, and a vast majority are harmless. However, occasionally, a thyroid nodule may be cancerous and require treatment.

Thyroid cancer: this disease is relatively common and has seen an increase in the number of incidents over the past couple of decades. The American Cancer Society estimates that around 63,000 new cases are diagnosed in the US each year, which makes it the 8th most common form of cancer as well as the fastest-growing form. Thyroid cancer comes in form main types:

Papillary thyroid cancer: makes up around 80% of all thyroid cancer cases. More women are affected by this type of thyroid cancer than men. It is also more commonly found in younger individuals.

Follicular thyroid cancer: makes up around 15% of all thyroid cancers. It is a more aggressive form of cancer, and older women tend to be at increased risk.

Anaplastic thyroid cancer: makes up around 2% of all thyroid cancers and tends to be found mostly in older women. It is hard to treat and tends to be aggressive.

Medullary thyroid cancer (MTC): makes up around 3% of all thyroid cancers. It is malignant and may spread past the thyroid. It can be hard to treat if not detected early. Excess calcitonin is produced by MTC and might be found by itself or linked along with other types of endocrine cancers within a syndrome, which is referred to as the multiple endocrine neoplasia syndrome. Cells that produce calcitonin are different from cells that produce thyroid hormone. They can increase in number, which results in the c-cell hyperplasia disorder. The condition is benign and produces excess calcitonin as well. It might progress into becoming medullary thyroid cancer sometimes.

Lymphoma is a tumor that is made up of lymphocytes (these are cells that produce immunity out of viruses and bacteria. It can take place inside the thyroid also.

Laboratory Tests

Usually, the first test that will be ordered by a healthcare practitioner for detecting thyroid dysfunction will be a thyroid-stimulating hormone (TSH) test. If there is an abnormal TSH level, usually a free thyroxine test will be ordered by the healthcare practitioner so that the diagnosis can be confirmed.

T4 is not real soluble inside the blood. Therefore, serum proteins carry it. A small percentage of overall T4 isn’t bound to protein. That fraction is biologically active. Laboratories in the past estimated free T4 concentrations by measuring total T4 and determining binding protein levels. However, these days, it is a lot more common for free T4 to be estimated by laboratories directly through the use of immunoassay. 

At times, tests for triiodothyronine (T3), which is the other primary thyroid hormone, might also be ordered, or all the tests might be ordered as one thyroid panel.

TSH – Used for monitoring thyroid disorder treatments, screening newborn babies for hypothyroidism, and testing for both hyperthyroidism and hypothyroidism.

Free T4 – Used for monitoring thyroid disease treatment, screening newborn babies for hypothyroidism, and testing for both hyperthyroidism and hypothyroidism.

Free T3 – Mainly used for testing hyperthyroidism, particularly whenever free T4 isn’t elevated. Whenever individuals are iodine-deficient, more T3 is made by the thyroid than T4.

Other tests that might be conducted include the following:

Total T3 and total T4 might be needed still in certain rare cases.

Thyroid antibodies – Help with identifying autoimmune thyroid conditions and differentiating various kinds of thyroiditis.

Thyroid peroxidase (TPO) antibody – This is an autoimmune thyroid disease marker. It may be detected in Hashimoto thyroiditis or Grave’s disease. It can be especially useful with early Hashimoto thyroiditis since TSH is elevated while the remaining thyroid still can maintain healthy levels of free T4.

Thyroglobulin (TG) antibody – This is a marker for both Hashimoto thyroiditis and Grave’s disease. Thyroglobulin, where thyroid hormone is stored, is targeted by this antibody.

TSHR (Thyroid-stimulating hormone receptor antibodies – This is a Graves disease marker. There are two different ways that it can be measured:

TBII (Thyroid binding inhibitory immunoglobulin) -This assay the serum of a patient’s ability to block TSH from binding with receptors.

TSI (Thyroid-stimulating immunoglobulin) – This assay measures thyroid cell stimulation inside of a culture dish.

Some Grave’s disease patients have antibodies that only can be detected by one of the two approaches. Autoimmune antibodies of the TSH receptor may rarely cause hypothyroidism (instead of hyperthyroidism).

Calcitonin – Helps with detecting excessive production of calcitonin, which may happen with medullary and C-cell hyperplasia thyroid cancer.