What Is a Low Thyroid Level Number

How Doctors Diagnose Hypothyroidism

Diagnosis of an underactive thyroid is made based on a combination of blood tests, symptoms, and several other factors.

Hypothyroidism is evaluated and diagnosed by a physician, usually an endocrinologist or your primary care doctor. The doctor will take into account symptoms, signs, and more critically, blood test results when evaluating the possibility that your thyroid gland is underperforming — all of which can help identify both the cause and severity of the disease.

There are several types of hormones checked in a blood test to assess your thyroid status. The most definitive one is the TSH (thyroid-stimulating hormone). Often, physicians may also decide to check your level of free or total thyroxine (T4) to aid in the diagnosis.

Here's a closer look at the exams and tests doctors use to diagnose hypothyroidism.

Your doctor may check your thyroid status for an underactive thyroid by reviewing thyroid hormone levels. Photo: 123rf

Personal and Family History and Physical Exam

It's important to give your physician as many details as possible about your personal medical history, as well as your family history. Be sure to discuss:

• Your general state of health — particularly any changes you have noticed in your general overall health.

• Your family's health history — especially if a close relative has been diagnosed with hypothyroidism or any other thyroid-related issues.

• Whether you've ever had thyroid surgery or radiation to your neck to treat cancer.

• Any medicines you may be taking that could cause hypothyroidism (examples include amiodarone, lithium, interferon alpha, interleukin-2, or prior chemotherapy).

In addition to going over your history and medications, your physician will perform a thorough examination to look for physical signs of hypothyroidism, including:

• Evidence of dry skin

• Swelling around the eyes and legs

• Slower reflexes

• Slower heart rate

Symptom Check

Many of the symptoms of hypothyroidism are fairly common complaints found in people with a normally functioning thyroid gland ... so it can be hard to decipher if the symptoms a patient is experiencing are related to their thyroid function. One clue to whether your symptoms could be related to a thyroid condition is how long you have been experiencing them.

For example, have you always felt cold when others were warm, or is this a more recent development? Has your energy level only recently started to flag? If your signs and symptoms are relatively new, that may increase the chance that they could be thyroid-related.

Blood Tests for Hypothyroidism

Hypothyroidism can be detected by different blood tests, including:

T4 (Thyroxine) Test

This test measures your blood level of T4, one of the two key thyroid hormones (the other is T3). In combination with a TSH test, your T4 levels can tell your physician how your thyroid is functioning. Doctors sometimes order two different types of T4 test — free T4 and total T4 — which look for slightly different forms of the hormone.

TSH Test

This test measures your blood level of thyroid-stimulating hormone, or TSH, which is a hormone produced by the pituitary gland that tells (or "signals") the thyroid gland how much thyroid hormone (mainly T4, or thyroxine) to make.

As blood flows through the pituitary gland, special cells detect if there are adequate T4 levels in the body. If your T4 level is adequate, the pituitary sends the appropriate amount of TSH to the thyroid to maintain T4 levels in the normal range. If your T4 level is too low, the pituitary sends more TSH out telling the thyroid to make more T4. If your T4 level is too high, the pituitary sends less TSH out, telling the thyroid to make less T4. An abnormally high level of TSH could mean you have hypothyroidism.

An easy way to remember how the thyroid works: Think about supply and demand. As the T4 level falls, the TSH rises. As the T4 level rises, the TSH falls. However, not everyone with hypothyroidism has elevated levels of TSH.

What Is a High TSH Level?

0.4 mU/L to 4.0 mU/L is considered the reference ("normal") range (there may be a slight variation depending on the laboratory), and people who have a normally functioning thyroid gland usually fall within this range.

If TSH measures > 4.0 mU/L, a second test (T4) is performed to verify the results. TSH > 4.0/mU/L with a low T4 level indicates hypothyroidism.

If your TSH is > 4.0 mU/L and your T4 level is normal, this may prompt your physician to test your serum anti-thyroid peroxidase (anti-TPO) antibodies. When these antibodies are present, it may indicate an autoimmune thyroid disorder, which is a risk factor for developing hypothyroidism.  If you have these antibodies, your doctor will most likely perform a TSH test at least once per year.

Treating Hypothyroidism

If you are diagnosed with hypothyroidism, you can expect to be prescribed a thyroid hormone pill called levothyroxine to take once a day, preferably in the morning. This medication is a synthetic (made in a laboratory) form of T4 that is designed to be an exact replacement for the T4 that the human thyroid gland normally secretes. It comes in multiple strengths and your dosage may have to be adjusted slightly each month until you and your doctor find the correct dosage for you.

Synthroid is the most common brand name for levothyroxine, but most people today will receive the generic version of the tablets, which is the most cost-effective and the version most likely to be covered by your insurance plan. Read more about thyroid hormone replacement here.

Updated on: 10/06/21

What is Thyroid Hormone Replacement Therapy?

What Is a Low Thyroid Level Number

Source: https://www.endocrineweb.com/conditions/hypothyroidism/how-doctors-diagnose-hypothyroidism

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