- How the TSH is produced?
- Thyroid Gland Overview
- Why TSH should be checked?
- Blood Test for TSH
- Blood Sample Collection
- Preparation before Blood Sample Collection
- TSH Result’s Normal Range
- The “Old Normal Range”
- The “New Normal Range”
- What the TSH Value Means
- Normal TSH
- Low Values
- High Values
- Treatment for Hypothyroidism and Hyperthyroidism
- Hypothyroidism Treatment
- Hyperthyroidism Treatment
- How to Prevent Hypothyroidism and Hyperthyroidism
Thyroid stimulating hormone (TSH) is a formal name used for Thyrotropin . It is a hormone produced by the anterior pituitary gland.
Good to know about the Pituitary Gland
The pituitary gland is a small endocrine gland about the size of a pea that rests below the hypothalamus of the brain. It was historically referred to as the “master gland” because of its influence on other glands of the body such as the gonads, adrenal cortex and the thyroid gland. It consists of two lobes in humans: the anterior lobe and the posterior lobe. 
- Production of growth hormone.
- Produces hormones that act on different endocrine glands of the body
- Produces hormones that affects the kidneys and the muscles
- Regulation of the function of endocrine
- Stores hormones from the hypothalamus 
Figure 1: Pituitary Gland Location
How the TSH is produced?
When thyrotropin-releasing hormone (TRH) is released from the hypothalamus, TSH will be produced. The pituitary gland is then triggered by the TRH to release TSH. In effect, the TSH targets our thyroid gland to produce thyroid hormones namely T3 (triiodothyronine) and T4 (thyroxine) that help in controlling the metabolism of our body. 
T3 and T4 are important for the brain’s normal growth especially during children’s formative years. A child with a thyroid gland that is deficient in making thyroid hormone may later become mentally retarded.
Failure of the thyroid gland to respond to the TSH produced by the pituitary gland will result in an excess amount of TSH found in the blood. The cause of the thyroid to malfunction can be secondary to illness, or surgery.
Figure 2: Production of TSH
Thyroid Gland Overview
It is a butterfly-shaped gland that is situated below the Adam’s apple which you cannot feel when it’s normal in size. It also has one sole duty, the conversion of your iodine intake into thyroid hormones that help regulate the body’s metabolism, body temperature, growth and development. 
Figure 3: Location of Thyroid Gland
Why TSH should be checked?
- To ascertain if your thyroid gland is in a proper working condition.
- To check if the symptoms that you are experiencing such as tiredness, weight gain, constipation, dry skin, frequent menstrual period, or intolerance of cold are caused by hypothyroidism (under-active thyroid gland).
- To check if the symptoms that you are experiencing such as rapid heart rate, weight loss, diarrhea, nervousness, irregular menstrual period, or intolerance of hot are caused by hyperthyroidism (overactive thyroid gland).
- To find the cause of hypothyroidism. TSH level will help determine if it is caused by the damage on the thyroid gland or other factors (like problem in the hypothalamus or pituitary gland).
- For people with hypothyroidism, to keep track if the thyroid replacement therapy is still effective.
- To keep track if the function of the thyroid gland in people with hyperthyroidism who are undergoing treatment like antithyroid medicine, radiation therapy or surgery.
- To screen the newborn babies for congenital hypothyroidism.
- Diagnose and monitor infertility problems in females. 
Figure 4: Symptoms of Hypothyroidism
Blood Test for TSH
The TSH blood test is the test of choice in evaluating thyroid symptoms and/or function. It is frequently ordered preceding or along with a T4 test. Other tests that your doctor may order are thyroid antibodies (for thyroid disease that is suspected to be autoimmune-related) and T3 test.
Blood Sample Collection
- The blood sample may be obtained in 2 ways:
- Through a needle placed in a vein in an arm (for adults).
- From pricking the heel (for an infant). 
Preparation before Blood Sample Collection
No special preparation will be needed before the test but there are certain medications and circumstances that may affect the quality of the test. So it’s of utmost importance that you tell your doctor if you are taking any of the following medications or have undergone these tests:
- Lithium (Duralith or Carbolith)
- Methimazole (Tapazole)
- Propylthiouracil 
Had recent x-rays where iodine dye was used.
Had a test where a radioactive material was given.
Having a long term illness (chronic) or severe stress. 
TSH Result’s Normal Range
The “Old Normal Range”
Most doctors in the U.S. used the range of 0.5 mI/L to 5.0 mI/L. In this range, a low TSH (under 0.5 mI/L) indicated an overactive thyroid (hyperthyroidism), and a high TSH (over 5.0 mI/L) indicated an underactive thyroid (hypothyroidism). 
The “New Normal Range”
In 2003, the American Association of Clinical Endocrinologists (AACE) issued a press release to update changes in the TSH’s normal values. From the range of 0.5 mI/L to 5.0 mI/L they narrowed the margin of the target TSH level of 0.3 mI/L to 3.0 mI/L.It is for the AACE’s belief that this new range will result in proper diagnosis especially for people with subtle symptoms that are still untreated. 
Unfortunately, many traditional doctors are still not aware with this new update and stick with the old range.
Figure 6: The Comparison of the “Old” and “New” TSH Values
What the TSH Value Means
A normal TSH hormone level ranges from 0.5 mI/L to 5.0 mI/L in an adult. It indicates that signals coming from the pituitary gland go well with the activity of the thyroid gland. The doctors may use other side effects or signals you manifest alongside with your TSH level to determine if other issues are of concern.
- Hyperthyroidism (overactive thyroid gland).
- The pituitary gland is damaged that it is prevented from releasing TSH (secondary hypothyroidism).
- First three months of pregnancy.
- Too much thyroid medicine was taken during the course of treatment for an underactive thyroid gland.
- Hypothyroidism (underactive thyroid gland).
- Too much production of TSH due to tumor in the pituitary gland (rare).
- Not taking enough medication in the treatment of hypothyroidism.
- Insufficient dietary iodine.
- Recovery from a severe illness.
- Resistance from T4. 
Whether low or high, a TSH result that is out of the normal range should be addressed promptly. And to investigate further, additional tests will be needed to ascertain the cause of the abnormal value.
Figure 7: Thyroid Function Test Interpretation
Treatment for Hypothyroidism and Hyperthyroidism
Gradual replacement of thyroid hormone with Levothyroxine (a synthetic hormone).For patients who are having a surgery and with myxedema coma, rapid treatment is necessary. Levothyroxine and hydrocortisone therapy should be started intravenously. 
Treatment will depend on the severity of the symptoms and the cause. Hyperthyroidism could be treated with single approach or a combination of any of the following:
- Antithyroid medicine.
- Radioactive iodine (to stop the production of excess hormones or destroys the thyroid gland)
- Surgical removal of the thyroid gland.
- Beta-blockers like propranolol may be used to manage some symptoms like sweating, rapid heart rate and anxiety.
- Replacement pill will be taken by a person whose thyroid gland is destroyed by radiation therapy or is surgically removed. 
How to Prevent Hypothyroidism and Hyperthyroidism
There is no known way to prevent hypothyroidism but the screening tests conducted on newborns a day after their delivery can help to detect congenital hypothyroidism. Like hypothyroidism, there is no existing way to prevent hyperthyroidism but quitting smoking may cut your risk.