Thyroid Testing Demystified: Understanding TSH, T3, and T4 Levels

The thyroid gland is in charge of generating various hormones that are important for the body’s metabolic processes. So, the associated disorders with glad are highly subjective, too. The prevalence rate of self-reported thyroid gland disorder or goiter in National Family Health Survey IV (NFHS IV) in the year 2015–16 was 2.2%, while it reached upto 2.9% in NFHS-V in the year 2019–2021.

Have you ever wondered why these disorders occur in the first place? Well, the level of thyroid hormones like T3, T4, and TSH directly contribute to these issues. Thus, undergoing thyroid testing and receiving proper treatment is imperative to maintaining a healthy life. In this blog, we will demystify the world of thyroid testing, shedding light on the roles of TSH, T3, and T4 levels.

An Overview of Thyroid Functions

The thyroid gland, situated below the Adam’s apple, consists of two lobes connected by the isthmus. It secretes two primary hormones into the bloodstream: thyroxine (T4) and triiodothyronine (T3). T4 is converted into the biologically active T3, which regulates the body’s metabolism.

The pituitary gland, located below the brain, regulates the thyroid gland’s secretion of T4 and T3 as thyroid hormones. It senses blood thyroid hormone levels like a thermostat, secreting Thyroid-stimulating hormone (TSH) when it’re below normal. When thyroid hormone levels rise above normal, the pituitary gland stops secreting TSH, reducing thyroid production. This mechanism is similar to a thermostat in a living room.

What are Thyroid Function Tests?

Evaluating thyroid function is a crucial step in diagnosing and managing thyroid disorders. This process typically involves a series of thyroid blood tests that measure the levels of specific hormones produced by the thyroid gland and the pituitary gland, which regulates thyroid function.

The first hormone typically tested is thyroid-stimulating hormone (TSH). A normal TSH level is generally indicative of a properly functioning thyroid system. However, if the TSH level is abnormal, further testing of other hormones, such as thyroxine (T4) and triiodothyronine (T3), may be necessary.

Many laboratories adopt a “cascade” approach to thyroid hormone testing. If the initial TSH test reveals an abnormal result, additional tests for T4 and T3 levels will be performed automatically.

• The blood T4 level will be measured if the TSH level is higher than the reference range.
• The blood T4 and T3 levels will be measured if the TSH level is below the range of references.

Typically, Free T4 (FT4) and Free T3 (FT3), the “free” or active components of T4 and T3, are tested. Reference ranges that are typical for healthy individuals are:

These ranges serve as estimates and will differ depending on the laboratory for thyroid testing. Pregnant women should ideally use reference ranges derived from healthy members of the same population, as the serum TSH reference range during pregnancy varies from that of the general population.

Interpreting the Thyroid Test Results

Usually, a diagnosis is based on the TSH and T4 levels. T3 levels are considered when T4and TSH levels indicate hyperthyroidism or if your thyroid test results are normal but you exhibit hyperthyroidism-related symptoms.

Thyroid function tests typically follow these patterns when evaluating thyroid function:

Your doctor may advise dietary changes, such as taking vitamin and mineral supplements, even if the test results are normal.

If the test results reveal a thyroid issue, your physician may recommend medications. To monitor your situation, your doctor may also suggest thyroid testing regularly (usually once every three months).

When should Go for a thyroid Test?

If any of the following problems occur to you, schedule an appointment with your doctor, who may recommend thyroid testing:

• Signs of an underactive or hyperactive thyroid
• Thickening or swelling in the neck
• An irregular or rapid heartbeat
• Elevated cholesterol levels (which lead to atherosclerosis, or the accumulation of fat in the arteries)
• Osteoporosis, or thinned or brittle bones
• Infertility problems, irregular periods, low libido, and repeated miscarriages
• Autoimmune diseases in the family, such as type 1 diabetes, vitiligo, etc

Additionally, if you are

• Feeling ill post-childbirth
• Preparing for or having a pregnancy (and you have a history of type 1 diabetes, postpartum thyroiditis, or thyroid issues in your family or yourself)

Exceptional Cases for Thyroid Testing

Your physician may suggest thyroid testing in the following cases as well:

• Your thyroid disorder after diagnosis.
• You’ve previously received therapy (radioactive iodine, thyroid surgery, medication) for an overactive thyroid.
• Following surgery for head and neck cancer, you underwent radiation treatment to your head and neck.
• Before starting amiodarone, lithium, or alemtuzumab treatment, as well as for six to twelve months throughout and after treatment

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