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Thyroid Stimulating Hormone

(TSH)

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Blood

This test is for

Male, Female

Test Preparation

No special preparation required

Overview

What is TSH?

Thyroid Stimulating Hormone (TSH) is a hormone secreted into the blood by Pituitary gland. TSH signals thyroid gland (a small, butterfly-shaped gland located in front of the neck) to release the thyroid hormones into the blood. The Thyroid Stimulating Hormone (TSH) Test measures the levels of TSH in the blood.

Why is TSH done?

To diagnose any suspected thyroid diseases (Hypothyroidism or Hyperthyroidism)
To monitor the effect of treatment in patients with thyroid diseases, e.g. in case of hypothyroid patients receiving various thyroid hormone preparations: Low values are found in states of high doses
To screen for any thyroid diseases during pregnancy
To screen for any thyroid diseases in newborns

What does TSH Measure?

Thyroid Stimulating Hormone (TSH) test measures the amount of TSH in your blood which helps to find out if the thyroid gland is working normally or not. Low TSH levels indicate hyperthyroidism and high TSH levels indicate hypothyroidism.

In case of hyperthyroidism, the thyroid gland produces very high amounts of thyroid hormones (T3 and T4) and you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity towards heat, etc. In case of Hypothyroidism, there is a decrease in the production of thyroid hormones (T3 and T4) which may cause weight gain, fatigue, slow heart rate, increased sensitivity towards cold, depression, dry and thin hair, etc.

There is a feedback system in the body to maintain stable amounts of the thyroid hormones (T3 and T4) in the blood. TSH signals the thyroid gland to make and release the thyroid hormones (T3 & T4) into the blood when the level of thyroid hormones is low and can also signal the thyroid gland to lower the production of thyroid hormones when the level of thyroid hormones is very high. So, when the thyroid hormone (T3 and T4) levels decrease, the pituitary gland is stimulated to release TSH and this high TSH level, in turn, stimulates thyroid gland to release more thyroid hormone (T3 & T4) from the thyroid gland and the vice-versa happens when the thyroid hormone levels are very high.

Interpreting TSH results

Interpretations

The TSH normal range may vary from lab to lab.

The TSH normal range for different age groups is given below:

Patients (Age) TSH Normal Range

Premature Infants (28-36 Weeks)
1st Week of Life	0.20-27.90 mIU/L
Term Infants (>37 Weeks)
Serum or Cord Blood	1.00-39.00 mIU/L
1-2 Days	3.20-34.60 mIU/L
3-4 Days	0.70-15.40 mIU/L
5 Days-4 Weeks	1.70-9.10 mIU/L
1-11 Months	0.80-8.20 mIU/L
1-19 Years	0.50-4.30 mIU/L
≥20 Years	0.40-4.50 mIU/L
Pregnancy
First Trimester	0.26-2.66 mIU/L
Second Trimester	0.55-2.73 mIU/L
Third Trimester	0.43-2.91 mIU/L

If your TSH level is increased, it usually indicates that you have hypothyroidism. Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism.
If your TSH level is decreased, it usually indicates hyperthyroidism. Graves' disease, multinodular goiter, toxic nodule are some of the common causes of hyperthyroidism.

Note: TSH normal range levels show circadian variation (fluctuates during the 24-hour cycle), reaching peak levels between 2-4 am and are at a low between 6-10 pm.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about TSH

Frequently Asked Questions about Thyroid Stimulating Hormone

Q. What are the symptoms of Hyperthyroidism?

Symptoms of Hyperthyroidism include: Rapid heartbeat (tachycardia) — commonly more than 100 beats/minute — irregular heartbeat (arrhythmia) or pounding of your heart (palpitations), sudden weight loss, nervousness, anxiety, irritability, tremor (usually a fine trembling in your hands and fingers), changes in menstrual patterns, increased sensitivity towards heat, changes in bowel patterns (especially more frequent bowel movements), an enlarged thyroid gland (goiter) which may appear as a swelling at the base of your neck, increased appetite, sweating, fatigue, muscle weakness, sleep disturbances, skin thinning, fine and brittle hair.

Q. What is Hypothyroidism?

Hypothyroidism, also called underactive thyroid or low thyroid is a condition in which the thyroid gland does not produce enough thyroid hormones. It can be commonly caused by intake of low iodine diet or Hashimoto's thyroiditis (an autoimmune disease). Less common causes include previous treatment with radioactive iodine, injury to the pituitary gland which secretes TSH, intake of certain medicines, previous thyroid surgery, or a lack of a functioning thyroid gland at birth.

Q. What are the symptoms of Hypothyroidism?

Hypothyroidism can cause symptoms such as tiredness (fatigue), hoarseness, constipation, feeling cold, dry skin, dry and thin hair, puffy face, weight gain, and muscle weakness. Along with that, one may experience decreased sweating, depression, slowed heart rate, increased blood cholesterol levels, pain, and stiffness in your joints, impaired memory, problems of infertility or menstrual changes, muscle stiffness, aches, and tenderness.

Q. What additional tests your doctor may ask for in case the TSH levels are not in the normal range?

If the TSH levels are not in the normal range, your doctor may ask for the following tests to establish the diagnosis of a suspected disease: T4 thyroid hormone test, T3 thyroid hormone test, Thyroid Hormone Binding Globulin (THBG) test, and Thyroid profile.

Q. What are the causes of high TSH in a newborn?

Congenital hypothyroidism is an important cause of elevated thyroid-stimulating hormone (TSH) in newborns. Other causes of an elevated TSH include transient hypothyroidism due to neonatal illness, premature birth, iodine excess or deficiency. High TSH can also be seen in case the mother is taking some medicines that could affect thyroid hormone levels or the mother has some underlying thyroid disease.

Q. How can hyperthyroidism affect a pregnant woman and her baby?

An untreated hyperthyroidism during pregnancy can lead to miscarriage, premature birth, low birth weight of the baby, preeclampsia (a very high rise in blood pressure in late pregnancy), thyroid storm (a sudden, severe worsening of symptoms of hyperthyroidism) and congestive heart failure.

Q. Are there any special precautions that need to be taken before the test?

Inform the doctor if you are taking any medicine or herbal product since some medicines like birth control pills, estrogen, Lithium, Prednisone, Amiodarone, etc. might interfere with the test results. A recent X-ray with iodine dye (contrast) or test using radioactive materials may also affect the results. Moreover, TSH levels show circadian variation (fluctuates during the 24 hour cycle) hence, sample for TSH test should be given at the same time in follow up cases.

Q. How can hypothyroidism affect a pregnant woman and her baby?

An untreated hypothyroidism during pregnancy can cause preeclampsia (a very high rise in blood pressure in late pregnancy), anemia, miscarriage, low birth weight of the baby, stillbirth (death or loss of a baby before or during delivery) and rarely, congestive heart failure. These problems are noticed mostly as a result of severe hypothyroidism. The mother’s thyroid hormones play an important role in the development of the baby’s brain and nervous system. Untreated hypothyroidism, especially during the first trimester can cause low IQ and can hinder the baby’s normal development.

Q. How is the blood sample taken?

The healthcare provider takes a blood sample from the arm. The site from where the blood is to be withdrawn is cleaned with a swab of rubbing alcohol. This is then followed by inserting a small needle which has a tube attached to it for collecting blood. Once the sufficient blood for analysis is withdrawn, the needle is removed. The site is then covered with a gauze pad.

Q. Is there any risk associated with the withdrawal of blood sample procedure?

As such there is no risk but in few cases, bruising, bleeding, and infection at the puncture site can be seen. In very few cases, there can be swelling of the vein after the blood is withdrawn.

Q. What is Hyperthyroidism?

Hyperthyroidism is a condition in which the thyroid gland is overactive and there is an increased production of thyroid hormones by the thyroid gland. Causes of Hyperthyroidism include Graves’ disease, multinodular goiter, thyroid nodules, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. Diagnosis of this condition can help to relieve the symptoms and prevent long-term complications.

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