Biotin (vitamin B7) should not be taken for 2 days before blood is drawn for accurate thyroid function testing.

Medications That Interfere with Thyroid Function Testing

Terminology

Pituitary Gland

Your thyroid is controlled by a gland in your brain called the pituitary gland.

The pituitary gland makes thyroid-stimulating hormone (TSH).

Biomolecules

Thyrotropin-Releasing Hormone

TRH

Produced by neurons in the hypothalamus.

Stimulates the release of thyroid-stimulating hormone (TSH).

Thyroid Peroxidase TPO

An enzyme expressed mainly in the thyroid.

Used by the thyroid gland to make thyroid hormones (T4 and T3) and store iodine in the body.

Thyroglobulin Tg

A precursor to thyroid hormones that is produced by the thyroid gland.

Thyroglobulin is a large protein used by the thyroid gland to make thyroid hormones (T4 and T3) and store iodine in the body.

Thyroid Stimulating Hormone TSH

Prompts the thyroid gland to increase hormone production.

Triiodothyronine

The T3 hormone.

Thyroxine

The T4 hormone.

Antibody Ab

Also known as immunoglobulins.

A large protein used by the immune system to identify and neutralize antigens such as those that exist on bacteria and virus cells, including those that cause disease.

Each individual antibody recognizes one or more specific antigens, and antigens (a portmanteau of "antibody generator") of virtually any size and chemical composition can be recognized.

Pathologies

Grave's Disease

Grave's disease is an autoimmune disorder that affects the thyroid gland and causes hyperthyroidism.

Hashimoto's Disease

Hashimoto's disease is an autoimmune disorder that affects the thyroid gland and causes hypothyroidism.

Diagnostic Biomarkers

Thyroid Stimulating Hormone TSH

TSH tells your thyroid how much thyroid hormone it needs to make.

• Too much TSH may signal your thyroid gland to produce too many hormones.

• Too little TSH may not signal to your thyroid gland to produce enough hormones.

Free T4

Measures the amount of T4 available to the cells and tissues.

Total T4

Measures the total amount of T4 produced by the thyroid gland.

Total T3

Measures the total amount of T3 produced by the thyroid gland.

T3 testing rarely is helpful in the hypothyroid patient, since it is the last test to become abnormal. Patients can be severely hypothyroid with a high TSH and low FT4 or FTI, but have a normal T3.

Free T3

Measures the amount of T3 (the active form of the hormone) available to the cells and tissues.

Measurement of free T3 is possible, but is often not reliable and therefore not typically helpful.

Reverse T3

Measures the non-functioning form of the active hormone T3.

In healthy, non-hospitalized people, measurement of reverse T3 does not help determine whether hypothyroidism exists or not, and is not clinically useful.

Antibodies

Thyroglobulin Antibody TgAb

More suggestive of Hashimoto's disease.

Thyroid Peroxidase Antibody TPOAb

Indicative of Hashimoto's disease, Grave's disease, and possibly thyroid cancer.

Thyroid-Stimulating Hormone Receptor Antibody TSHR-Ab

Strongly linked to Graves' disease.

Thyroid Stimulating Immunoglobulin TSI

Strongly linked to Graves' disease.

Thyrotropin Receptor Antibody TRAb

Strongly linked to Graves' disease.

Diagnostic Testing

Hormone Testing

Good for maintenance.

Antibody Testing

Good for diagnosing thyroid autoimmunity.

Less important to get rechecked often.

Life Extension

Comprehensive Thyroid Panel TSH, T4, Free T4, Free T3, Reverse T3, TgAb, TPOAb

Good for maintenance.

Thyroid Panel with Reverse T3 TSH, T4, Free T4, Free T3, Reverse T3

Good for maintenance.

Thyroid Panel Blood Test TSH, T4, Free T4, Free T3

Good for maintenance.

Thyroid Antibody Panel Blood Test TgAb, TPOAb

Incomplete. Doesn't measure levels of thyroid hormones.

Quest Health

Comprehensive Thyroid Test Panel TSH, T4, Free T4, Free T3, TgAb, TPOAb

Too expensive.

Labcorp OnDemand

Standard Thyroid Test TSH, Free T4

Incomplete. Does not measure T3.

Too expensive.