Evidence-Based Supplement & Herb Guides

Calcitonin Blood Test: High Levels, Medullary Thyroid Cancer, C-Cells, and Results

Learn how the calcitonin blood test measures thyroid C-cell activity, why levels rise, how results relate to medullary thyroid cancer, and what follow-up may involve.

A calcitonin blood test measures a hormone made mainly by the thyroid gland’s parafollicular cells, better known as C-cells. The test is most useful...

Free T3 (Free Triiodothyronine) Test: High, Low, Normal Range, and Thyroid Results

Understand what a free T3 blood test measures, why levels may be high or low, how normal ranges vary, and when results help diagnose thyroid disease.

A free T3 test measures the small portion of triiodothyronine circulating without a binding protein. T3 is the thyroid hormone that acts most strongly...

Free T4 (Free Thyroxine) Test: High, Low, Normal Range, and Thyroid Results

Learn how a free T4 blood test helps identify hypothyroidism, hyperthyroidism, and pituitary disease, why ranges vary, and what high or low results may mean.

A free T4 blood test measures the unbound portion of thyroxine, the main hormone released by the thyroid gland. It is commonly paired with...

Free Thyroxine Index (FTI) Test: Thyroid Function, T4 Binding, and Results

Learn how the free thyroxine index combines total T4 and T3 uptake, what high or low FTI results suggest, and when binding proteins can affect interpretation.

The free thyroxine index, usually shortened to FTI or FT4I, is a calculated estimate of biologically available thyroxine. It combines a total T4 result...

Graves Disease Blood Test Panel: TSH, Free T4, T3, TRAb, TSI, and Results

Understand the Graves disease blood test panel, including TSH, free T4, T3, TRAb, and TSI patterns used for diagnosis, treatment monitoring, and pregnancy care.

A Graves disease blood test panel usually combines thyroid function tests with antibodies that target the TSH receptor. The typical untreated pattern is a...

Hashimoto Thyroiditis Blood Test Panel: TSH, Free T4, TPOAb, TgAb, and Results

Understand the Hashimoto thyroiditis panel, including TSH, free T4, TPOAb, and TgAb patterns, what positive antibodies mean, and when treatment is needed.

A Hashimoto thyroiditis blood test panel evaluates thyroid function and looks for evidence of thyroid autoimmunity. TSH and free T4 show whether the thyroid...

Hyperthyroidism Blood Test Panel: Low TSH, T3, T4, TRAb, TSI, and Results

Understand a hyperthyroidism blood test panel, including low TSH, high T3 or T4, TRAb and TSI results, causes, interference, and follow-up.

A hyperthyroidism blood test panel checks whether the body has too much thyroid hormone and helps identify why. The usual starting tests are thyroid-stimulating...

Hypothyroidism Blood Test Panel: High TSH, Free T4, TPOAb, TgAb, and Results

Learn how high TSH, low or normal free T4, TPOAb, and TgAb results identify hypothyroidism, Hashimoto thyroiditis, treatment needs, and follow-up.

A hypothyroidism blood test panel checks whether the body has too little thyroid hormone and whether autoimmune thyroid disease is the likely cause. In...

Neonatal TSH Test: Congenital Hypothyroidism, Newborn Thyroid Screening, and Results

Learn how neonatal TSH screening detects congenital hypothyroidism, why timing matters, what high or borderline results mean, and how babies are treated.

A neonatal TSH test is part of newborn screening for congenital hypothyroidism, a condition in which a baby is born without enough thyroid hormone....

Reverse T3 (rT3) Test: High, Low, Normal Range, and Thyroid Conversion

Understand reverse T3 testing, including high and low results, assay ranges, illness effects, thyroid conversion claims, and why TSH and free T4 matter more.

A reverse T3 test measures an inactive metabolite made when the body converts thyroxine (T4). Reverse T3, abbreviated rT3, often rises during severe illness,...

T3 Uptake Test: Thyroid Hormone Binding, TBG, High and Low Results

Learn what the T3 uptake test measures, why high or low results reflect TBG and hormone binding, how FTI is calculated, and which modern tests help.

A T3 uptake test is an older thyroid blood test that estimates how many binding sites are available on proteins that carry thyroid hormones....

Thyroglobulin (Tg) Blood Test: Thyroid Cancer Follow-Up, High or Low Levels, and Results

Understand thyroglobulin testing after thyroid cancer, including high, low, or undetectable Tg, TSH stimulation, TgAb interference, trends, and imaging.

A thyroglobulin blood test measures a protein made only by normal thyroid follicular cells and most differentiated thyroid cancer cells. Its main role is...

Thyroglobulin Antibody (TgAb) Test: Autoimmune Thyroid Disease and Results

Learn how thyroglobulin antibody results relate to Hashimoto and Graves disease, thyroid function, Tg assay interference, and thyroid cancer follow-up trends.

A thyroglobulin antibody test detects immune proteins directed against thyroglobulin, a protein made by thyroid follicular cells. TgAb is most often used for two...

Thyroid Antibody Panel: TPOAb, TgAb, TRAb, TSI, and Results

Understand TPOAb, TgAb, TRAb, and TSI results, including Hashimoto and Graves patterns, normal thyroid function, pregnancy, and cancer follow-up.

A thyroid antibody panel looks for immune proteins that react with the thyroid gland or its hormone-making machinery. The four names most often seen...

Thyroid Function Test Panel: TSH, Free T4, Free T3, Thyroid Antibodies, and Results

Learn how TSH, free T4, free T3, and thyroid antibodies fit together, what common result patterns mean, and when repeat testing or follow-up is needed.

A thyroid function test panel combines blood tests that show how the pituitary gland and thyroid are communicating. TSH is usually the starting test,...

Thyroid Hormone Replacement Monitoring Test: TSH, Free T4, Levothyroxine Dose, and Results

Learn how TSH and free T4 guide levothyroxine dosing, when to retest, and how missed doses, absorption, pregnancy, and interactions affect results.

Thyroid hormone replacement monitoring checks whether a levothyroxine dose is supplying enough T4 without causing excess. For most adults with primary hypothyroidism, TSH is...

Thyroid Peroxidase Antibody (TPOAb) Test: Hashimoto Thyroiditis, Graves Disease, and Results

Understand positive and negative TPOAb results, Hashimoto and Graves associations, normal thyroid function, pregnancy risks, and when follow-up is needed.

The thyroid peroxidase antibody test detects immune proteins directed against thyroid peroxidase, an enzyme the thyroid uses to make T4 and T3. A positive...

Thyroid Tests in Pregnancy: TSH, Free T4, TPOAb, Trimester Ranges, and Results

Understand pregnancy TSH, free T4, TPOAb, and TRAb results, trimester ranges, hypothyroid and hyperthyroid patterns, treatment monitoring, and postpartum care.

Thyroid testing in pregnancy usually begins with TSH and adds free T4 when TSH is outside the pregnancy-appropriate range or thyroid disease is strongly...

Thyroid-Stimulating Hormone (TSH) Test: High, Low, Normal Range, and Thyroid Function Results

Understand high, low, and normal TSH results, how free T4 and T3 change the meaning, and when repeat testing, treatment review, or urgent care is needed.

The thyroid-stimulating hormone test measures TSH, a pituitary hormone that tells the thyroid how much T4 and T3 to make. It is usually the...

Thyroid-Stimulating Immunoglobulin (TSI) Test: Graves Disease, Positive Results, and Meaning

Understand positive, negative, and borderline TSI results, how TSI differs from TRAb, and how the test guides Graves diagnosis, relapse assessment, and pregnancy care.

The thyroid-stimulating immunoglobulin test looks for antibodies that activate the thyroid’s TSH receptor. These stimulating antibodies can make the gland produce excessive T4 and...