What is TSH?

Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland in your brain. It signals your thyroid gland to produce thyroid hormones (T3 and T4), which regulate your metabolism, energy levels, body temperature, and heart rate. TSH is the most sensitive marker for evaluating thyroid function.

Why is it Important?

Thyroid disorders affect roughly 5% of the population. Because TSH responds to even small changes in thyroid hormone levels, it is the first-line test for detecting both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid). Untreated thyroid disorders can lead to weight changes, heart problems, and mood disturbances.

Normal Ranges

Group	Range	Unit
Adult	0.4 – 4.0	mIU/L
Pregnancy (1st trimester)	0.1 – 2.5	mIU/L
Pregnancy (2nd trimester)	0.2 – 3.0	mIU/L
Pregnancy (3rd trimester)	0.3 – 3.0	mIU/L

What Do Abnormal Results Mean?

High TSH (Hypothyroidism)

A high TSH indicates an underactive thyroid. Common causes include:

Hashimoto's thyroiditis (autoimmune)
Iodine deficiency
Previous thyroid surgery or radiation
Certain medications (lithium, amiodarone)
Pituitary gland disorders (rarely)

Symptoms: fatigue, weight gain, cold intolerance, constipation, dry skin, depression.

Low TSH (Hyperthyroidism)

A low TSH indicates an overactive thyroid. Common causes include:

Graves' disease (autoimmune)
Toxic multinodular goiter
Thyroiditis (inflammation)
Excessive thyroid medication
Excessive iodine intake

Symptoms: weight loss, rapid heartbeat, anxiety, tremors, heat intolerance, insomnia.

When Should You Get Tested?

TSH testing is recommended if you have symptoms of thyroid dysfunction, a family history of thyroid disease, or are pregnant or planning pregnancy. It is also part of routine screening for adults over 35, especially women, who are 5–8 times more likely to develop thyroid disorders.