Thyroid Panel

Thyroid tests measure how well your thyroid gland is functioning. The thyroid affects metabolism, energy, weight, mood, and nearly every organ system.

Educational Information Only

Thyroid test interpretation depends on context: pregnancy, medications, and illness all affect results. "Normal" TSH ranges are controversial—some patients have symptoms even within the normal range. Discuss your results and symptoms with your doctor.

Key insight: TSH alone may not tell the whole story. Thyroid antibodies (TPO) can be elevated for years before TSH becomes abnormal. If you have symptoms but "normal" TSH, consider asking for a complete panel including Free T3 and antibodies.

Quick Pattern Recognition

Hypothyroidism:TSH ↑ high, T4 ↓ low, T3 ↓ low

Hyperthyroidism:TSH ↓ low, T4 ↑ high, T3 ↑ high

Subclinical Hypo:TSH ↑ mildly high, T4 normal

Hashimoto's:TPO antibodies positive, TSH may be normal or high

Thyroid Function Tests

TSH (Thyroid Stimulating Hormone)

0.4 - 4.0 mIU/L

Measures: Pituitary hormone that tells the thyroid to produce hormones

High: Hypothyroidism (underactive thyroid) - the pituitary is working harder to stimulate a sluggish thyroid

Low: Hyperthyroidism (overactive thyroid) - the pituitary backs off because thyroid is already overproducing

Most sensitive screening test. TSH rises before T4 drops, catching early hypothyroidism. Note: "normal" range is controversial; some experts prefer <2.5 mIU/L.

American Thyroid Association - TSH|Full test guide

Free T4 (Free Thyroxine)

0.8 - 1.8 ng/dL

Measures: Active thyroid hormone available to tissues (not bound to proteins)

High: Hyperthyroidism, excessive thyroid medication, thyroiditis

Low: Hypothyroidism, pituitary dysfunction

T4 is the main hormone produced by the thyroid. "Free" means unbound and active. Confirms hypothyroidism when TSH is high.

AACE - Thyroid Guidelines

Free T3 (Free Triiodothyronine)

2.3 - 4.2 pg/mL

Measures: The most active thyroid hormone (converted from T4 in tissues)

High: Hyperthyroidism, T3 thyrotoxicosis

Low: Hypothyroidism, T4-to-T3 conversion problems, severe illness

T3 is 4x more potent than T4. Some patients have normal T4 but low T3 conversion. Often not included in basic panels but important for complete picture.

Endocrine Society

Total T4

5.0 - 12.0 μg/dL

Measures: All T4 in blood (bound + free)

High: Hyperthyroidism, pregnancy, estrogen therapy (increases binding protein)

Low: Hypothyroidism, protein abnormalities

Affected by protein levels. Free T4 is more accurate but Total T4 is sometimes used as a screening test.

MedlinePlus - T4 Test

Total T3

80 - 200 ng/dL

Measures: All T3 in blood (bound + free)

High: Hyperthyroidism (often elevated before T4 in early disease)

Low: Hypothyroidism, severe illness (sick euthyroid)

Useful for diagnosing hyperthyroidism. May be elevated even when T4 is normal in early Graves' disease.

MedlinePlus - T3 Test

Thyroid Antibody Tests

Antibody tests identify autoimmune thyroid disease (Hashimoto's, Graves'). They're not always included in a "thyroid panel" — you may need to request them specifically.

TPO Antibodies (Anti-TPO)

Thyroid Peroxidase Antibodies

<35 IU/mL (lab-dependent)

Present in ~95% of Hashimoto's thyroiditis. Can be elevated years before TSH becomes abnormal. Higher levels associated with higher risk of progression to hypothyroidism.

NCBI - Hashimoto Thyroiditis