What Is a Thyroid-Stimulating Hormone Test?

In most cases, if you exhibit signs of an overactive or underactive thyroid gland, your doctor will ask you to take a thyroid stimulating hormone test.

The thyroid is a butterfly-shaped gland located at the front of the neck. The pituitary gland regulates thyroid function by producing TSH and releasing it into circulation. TSH stimulates the thyroid gland to create thyroid hormones (T3 and T4). 

This process regulates how rapidly your body uses energy, produces proteins, and controls other vital tasks such as:

• Body temperature
• Heart rate
• Breathing
• Skin moisture
• Muscle contraction
• Weight gain or loss
• Brain development
• Cholesterol levels
• Menstruation
• Nervous system function

Overactive thyroid (hyperthyroidism)

Low TSH levels may indicate that the thyroid gland is overactive, a condition known as hyperthyroidism. Symptoms may include:

• Increased appetite
• Irregular heartbeat
• Palpitations (fluttering or pounding heartbeat)
• Unintentional weight loss
• More frequent bowel movements
• Anxiety or nervousness
• Sweating
• Heat intolerance
• Tremors
• Difficulty sleeping
• Fatigue

Underactive thyroid (hypothyroidism)

High TSH levels in the blood may indicate that the thyroid gland is not working hard enough, causing the pituitary to continue producing TSH. Hypothyroidism may cause symptoms such as:

• Weight gain
• Fatigue
• Increased sensitivity to cold
• Thinning and or dry hair
• Hair loss
• Goiter (enlarged thyroid gland)
• Muscle weakness
• Muscle aches and pains
• Joint pain and stiffness
• Elevated cholesterol levels
• Constipation
• Irritability
• Brain fog
• Memory problems
• Depression
• Slower than normal heart rate
• Dry skin
• Facial puffiness
• Hoarseness
• Cold intolerance
• High blood cholesterol levels
• Heavy or irregular menstrual cycles

Other conditions

Thyroid disorder symptoms can be mild, moderate, or severe, and they quite often mimic other medical conditions. Your doctor may recommend a thyroid function test if you are:

• Taking lithium
• Entering menopause
• Pregnant 
• Have a family history of thyroid or pituitary issues
• Have had recent neck surgery

There are no preparations required for TSH testing. However, talk to your doctor if you have any underlying medical conditions or if you are taking any medications or supplements. 

If your doctor has prescribed certain other tests along with TSH, you may need to fast beforehand. Thus, ask your doctor if you need any special preparation before the test.

The test is performed in the same manner as a blood test:

• A nurse or healthcare professional will wrap an elastic band around your arm to make the veins visible so that the needle can be inserted. 
• A disinfectant solution will be used to clean the area from where the blood will be drawn. The blood will then be drawn using a needle inserted into your vein. 
• After the needle is removed, a cotton ball is used to apply pressure to the area where the blood is drawn. 

This process only takes a few minutes, and the test overall is generally considered safe.

A thyroid-stimulating hormone test does not carry risks, but a few people may experience side effects that include:

• Multiple punctures to locate veins
• Slight pain or bruise at the spot where the needle is inserted which will fade away quickly
• Minor bleeding after the removal of the needle 
• Excessive bleeding if you have bleeding disorders or take blood thinners
• Signs of bruising for a couple of days
• Dizziness, nausea, and even possible loss of consciousness at the sight of blood
• Hematoma (blood buildup under the skin)
• Infection (a slight risk any time the skin is broken)

Results of thyroid-stimulating hormone tests are usually available within 1-2 days. TSH levels are generally the first sign of a thyroid problem, but they are not the only indicator. Although abnormal TSH levels can indicate a problem,  additional thyroid tests are required to confirm that the problem is with the thyroid.

Each lab has a different normal range. Your lab report should include the range used by your lab for each test. The normal range is only a guideline. Your results will also be evaluated by your doctor based on your age, health, and other factors. A value that is outside of the normal range can be normal for you as per your doctor’s interpretation.

An optimal TSH range is defined as anything between 0.5 and 4.5 mIU/L, although many experts use 3.5 mIU/L as the upper limit for deciding whether to order a more detailed comprehensive thyroid panel. Normal ranges for TSH may vary slightly by lab and academic association:

• National Health and Nutrition Examination Survey III: 0.45 to 4.120 mIU/L.
• National Academy of Clinical Biochemists: 2.5 mIU/L. However, if that were to be adopted as the standard, millions of Americans would be diagnosed with hypothyroidism. 
• American Association of Clinical Endocrinologists and American Thyroid Association: 0.45 to 4.12 mIU/L. Therefore, most labs go by a range with a limit of 4 mIU/L with a suggestion for “at-risk” with anyone above 2.5 to 3.0 mIU/L. 

A slightly elevated TSH level may not necessitate treatment. Your doctor will consider any symptoms you may be experiencing, as well as the results of other tests, to determine whether treatment is required. 

High TSH levels may be caused by

• Hypothyroidism and Hashimoto’s thyroiditis
• Not taking enough thyroid hormone medicine for the treatment of an underactive thyroid gland

Low TSH levels may be caused by:

• Graves’ disease
• A noncancerous (benign) tumor called a toxic nodule
• Secondary hypothyroidism (damage to the pituitary gland that prevents it from making TSH)
• Taking too much thyroid medicine for the treatment of an underactive thyroid gland

In most cases, lifestyle management, dietary changes, and managing stress levels can help mild thyroid problems. Doctors may recommend medications only if necessary.

• Underactive thyroid: Hypothyroidism is normally treated by taking synthetic thyroid hormones daily to restore normal blood levels. As a result, you will feel more energetic and will be able to lose any weight you may have gained. Your TSH levels will be checked every 2-3 months to ensure that you are getting the right dosages. If the results are within normal ranges, your TSH will be tested once a year.
• Overactive thyroid: Treatment options include radioactive iodine, antithyroid medications, beta-blockers, and surgical removal of the gland. If you have an overactive thyroid, you will need TSH testing on a regular basis to monitor your levels.

Some doctors only use TSH testing to diagnose low or high thyroid function. Although some guidelines recommend a TSH range of 0.4 to 4.5 mIU/mL, some people may be experiencing hypothyroidism symptoms at TSH levels above 3 due to occult Hashimoto’s disease or other issues, so it is always a good idea to perform a thyroid panel that includes not only TSH but also free T3 and free T4. 

There is an ongoing debate about whether it is medically sound to rely solely on the TSH test to the exclusion of clinical symptoms and other tests such as free T4, free T3, and antibodies tests. That is a contentious issue that is unlikely to be resolved for many years. Currently, however, the majority of physicians rely almost entirely on the TSH test to diagnose thyroid disease and monitor treatment effectiveness.

Additional thyroid tests are required to confirm that the problem is with the thyroid. To ensure that the levels of T3 and T4 in the body match the amount of TSH secreted, these tests would include total T4, T3U, and T7 or FTI tests. If thyroid hormone levels are found to be within the normal range, a pituitary gland problem may exist. Tests to ensure that the pituitary gland is functioning properly may be required.

If you are older than 35 and in good health, your doctor may advise you to have this test done once a year or every other year. If you have a thyroid disorder, your doctor may recommend that you have this test every 3 months to once a year, depending on your clinical condition.