Thyroid Stimulating Hormone (TSH)
Also known as: TSH, Thyrotropin, Thyroid Function Test
The TSH test measures the level of thyroid-stimulating hormone in your blood. TSH is produced by the pituitary gland and tells the thyroid gland to make and release thyroid hormones (T3 and T4). It is the most sensitive and commonly used test for evaluating thyroid function.
Purpose
Screening for thyroid disorders (hypothyroidism and hyperthyroidism). Evaluating symptoms such as unexplained weight changes, fatigue, hair loss, cold or heat intolerance, depression, or anxiety. Monitoring thyroid hormone replacement therapy (levothyroxine dosing). Newborn screening for congenital hypothyroidism. Evaluating fertility issues — thyroid disorders can affect ovulation and pregnancy.
Preparation
No fasting is required. If you take thyroid medication (levothyroxine), your doctor may advise you to delay your dose until after the blood draw, as it can temporarily affect results. Biotin (vitamin B7) supplements can interfere with some TSH assays — stop biotin 2–3 days before testing.
Procedure
A standard blood draw from a vein in your arm. Blood is sent to the laboratory for immunoassay analysis. Takes about 5 minutes.
Normal Range
Adults: 0.4–4.0 mIU/L (some labs use 0.5–5.0 mIU/L). Pregnancy: Lower ranges apply — first trimester 0.1–2.5 mIU/L, second trimester 0.2–3.0 mIU/L, third trimester 0.3–3.0 mIU/L. Note: 'Normal' ranges are debated; some endocrinologists consider levels above 2.5 worth monitoring.
Abnormal Results
High TSH usually indicates hypothyroidism (underactive thyroid) — the pituitary is producing more TSH to try to stimulate a sluggish thyroid. Common causes: Hashimoto's thyroiditis, thyroid surgery, radiation, iodine deficiency. Low TSH usually indicates hyperthyroidism (overactive thyroid) — the pituitary reduces TSH because thyroid hormone levels are already high. Common causes: Graves' disease, thyroid nodules, thyroiditis, excess thyroid medication.
Risks
Minimal — standard venipuncture risks.
Turnaround Time
Results typically available in 1–2 days.
Estimated Cost
$25–$75 without insurance. Covered by most insurance plans when medically indicated.
Frequently Asked Questions
What is a Thyroid Stimulating Hormone (TSH) test?▼
The TSH test measures the level of thyroid-stimulating hormone in your blood. TSH is produced by the pituitary gland and tells the thyroid gland to make and release thyroid hormones (T3 and T4). It is the most sensitive and commonly used test for evaluating thyroid function.
What is the normal range for a Thyroid Stimulating Hormone (TSH)?▼
Adults: 0.4–4.0 mIU/L (some labs use 0.5–5.0 mIU/L). Pregnancy: Lower ranges apply — first trimester 0.1–2.5 mIU/L, second trimester 0.2–3.0 mIU/L, third trimester 0.3–3.0 mIU/L. Note: 'Normal' ranges are debated; some endocrinologists consider levels above 2.5 worth monitoring.
How do I prepare for a Thyroid Stimulating Hormone (TSH)?▼
No fasting is required. If you take thyroid medication (levothyroxine), your doctor may advise you to delay your dose until after the blood draw, as it can temporarily affect results. Biotin (vitamin B7) supplements can interfere with some TSH assays — stop biotin 2–3 days before testing.
What do abnormal Thyroid Stimulating Hormone (TSH) results mean?▼
High TSH usually indicates hypothyroidism (underactive thyroid) — the pituitary is producing more TSH to try to stimulate a sluggish thyroid. Common causes: Hashimoto's thyroiditis, thyroid surgery, radiation, iodine deficiency. Low TSH usually indicates hyperthyroidism (overactive thyroid) — the pituitary reduces TSH because thyroid hormone levels are already high. Common causes: Graves' disease, thyroid nodules, thyroiditis, excess thyroid medication.
Related Lab Tests
Complete Blood Count (CBC)
Hematology
A complete blood count (CBC) is one of the most commonly ordered blood tests. It measures the types and numbers of cells in your blood, including red blood cells, white blood cells, and platelets. A CBC provides a broad snapshot of your overall health and can help detect a wide range of disorders.
Basic Metabolic Panel (BMP)
Chemistry
The basic metabolic panel is a group of 8 blood tests that measure your blood sugar (glucose), electrolyte and fluid balance, and kidney function. It provides critical information about your body's chemical balance and metabolism.
Lipid Panel
Chemistry
A lipid panel measures the levels of fats (lipids) in your blood, including cholesterol and triglycerides. It is a key tool for assessing your risk of cardiovascular disease, including heart attack and stroke. Regular lipid screening is recommended for all adults.
Medical Disclaimer
This lab test information is for educational purposes only and should not replace professional medical advice. Lab results should always be interpreted by a qualified healthcare provider who knows your complete medical history. Normal ranges may vary between laboratories.