Hormone Journal

TSH, T3, and T4

Also known as: thyroid panel, thyroid stimulating hormone

Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-17

TSH, T3, and T4 are the three blood markers used together to screen for and diagnose thyroid disorders such as hypothyroidism and hyperthyroidism.

What it is

TSH, T3, and T4 are the three blood markers used together to screen for and diagnose thyroid disorders such as hypothyroidism and hyperthyroidism. TSH (thyroid-stimulating hormone) is produced by the pituitary gland at the base of the brain. T3 (triiodothyronine) and T4 (thyroxine, or tetraiodothyronine) are the hormones the thyroid gland itself releases. Together, they regulate metabolism, heart rate, body temperature, growth, and energy use throughout the body.

Causes and mechanism

The hypothalamus (a region of the brain) releases TRH (thyrotropin-releasing hormone), which signals the pituitary to secrete TSH. TSH then travels through the bloodstream to the thyroid gland, where it triggers the production and release of T3 and T4. T4 makes up more than 80% of what the thyroid secretes, but T3 is the biologically active form. Most T3 in the body comes from the conversion of T4 in peripheral tissues such as the liver and kidneys — not directly from the thyroid. When T3 and T4 levels rise, they feed back to suppress TSH; when they fall, TSH rises. This loop is why TSH shifts earlier and more sensitively than T3 or T4 when thyroid function changes.

Symptoms and diagnosis

Hypothyroidism (underactive thyroid) presents with fatigue, weight gain, cold intolerance, constipation, dry skin, and slowed heart rate. Hyperthyroidism (overactive thyroid) causes weight loss, heat intolerance, palpitations, anxiety, and tremor. Because symptoms overlap with many other conditions, blood testing is required to confirm a diagnosis.

Testing sequence:

  • TSH alone is the recommended first-line screen for most patients. A normal TSH (roughly 0.4–4.0 mIU/L in most labs) generally rules out significant thyroid dysfunction.
  • Free T4 (fT4) is added when TSH is abnormal, to distinguish primary from secondary thyroid disease and to grade severity.
  • Free T3 (fT3) is measured selectively — for example, in suspected T3-toxicosis or when monitoring patients on combination therapy. Routine T3 testing adds little in straightforward cases.
  • Total T3/T4 (bound + free) are less commonly used because binding-protein changes (pregnancy, liver disease, certain medications) can distort results without reflecting true hormone activity.

Reference ranges vary by laboratory and population, so always interpret results against the specific lab's reference interval.

Treatment options

ConditionFirst-line treatment
Primary hypothyroidismLevothyroxine (synthetic T4), dose titrated to normalize TSH
Hyperthyroidism (Graves' disease)Antithyroid drugs (methimazole, propylthiouracil), radioactive iodine, or thyroidectomy
Subclinical hypothyroidism (elevated TSH, normal fT4)Treatment is individualized; guidelines generally recommend treatment when TSH exceeds 10 mIU/L or symptoms are present

Some patients on levothyroxine report persistent symptoms despite normal TSH. Researchers debate whether adding T3 (liothyronine) improves outcomes; current American Thyroid Association guidelines do not recommend routine combination therapy, but acknowledge that a subset of patients may benefit. Evidence from randomized trials is limited and results are mixed.

When to see a clinician

Request a TSH test if you have unexplained fatigue, significant weight change, heart-rate irregularities, or a family history of thyroid disease. Seek prompt care if you develop a rapidly enlarging neck lump, severe palpitations, or signs of thyroid storm (fever, confusion, rapid heart rate). Pregnant people should have TSH checked early in pregnancy, as even subclinical hypothyroidism carries fetal risk. Anyone already on thyroid medication should have TSH rechecked 6–8 weeks after any dose change, then annually once stable.

FAQs

What is the difference between free T3/T4 and total T3/T4?

Free T3 and free T4 measure only the unbound, biologically active hormone circulating in the blood. Total T3 and T4 include hormone bound to carrier proteins like TBG (thyroxine-binding globulin). Because binding-protein levels change during pregnancy, with oral contraceptive use, or in liver disease, total values can appear abnormal even when thyroid function is normal. Most guidelines recommend free hormone measurements for this reason.

What TSH level is considered abnormal?

Most laboratories set the normal TSH range at approximately 0.4–4.0 mIU/L, though the exact cutoffs vary by lab and by age — older adults often have slightly higher values. A TSH above 4.0–5.0 mIU/L suggests hypothyroidism; a TSH below 0.4 mIU/L suggests hyperthyroidism. Subclinical hypothyroidism is typically defined as a TSH between 4.5 and 10 mIU/L with a normal free T4. Always interpret your result against your specific lab's reference range.

Can I have normal TSH but still have thyroid symptoms?

Yes, and this is a common clinical challenge. A normal TSH makes significant thyroid dysfunction unlikely, but it does not rule out every thyroid-related problem. Some researchers argue that a subset of patients feel better with TSH in the lower half of the normal range (around 1–2 mIU/L), though evidence for this target is not conclusive. If symptoms persist with a normal TSH, clinicians may check free T3, thyroid antibodies (TPO-Ab, TgAb), or investigate non-thyroid causes.

How often should a thyroid panel be repeated?

For healthy adults with no known thyroid disease, routine screening is not universally recommended, though some guidelines suggest checking TSH once in midlife. People on stable levothyroxine therapy should have TSH checked annually. After any dose adjustment, recheck TSH in 6–8 weeks because it takes that long for levels to fully equilibrate. Pregnant people need TSH monitoring each trimester.

Is a thyroid panel covered by insurance?

In the United States, a TSH test ordered for a documented clinical indication (symptoms, monitoring of a known condition) is covered by most insurance plans, including Medicare and Medicaid, typically with only a copay or deductible cost. Adding free T4 or free T3 is also usually covered when TSH is abnormal. Routine screening without symptoms may be billed differently depending on the plan. Check with your insurer before ordering an expanded panel, as out-of-pocket costs for a full thyroid panel can range from $30 to over $200 without coverage.

Sources

All glossary termsUpdated 2026-05-17