How to Measure Thyroid Levels

It is critical that they thyroid gland produce the correct amount of thyroid hormones for the body to function properly.  When too little thyroid hormone is present in the body a condition known as hypothyroidism results.  When there is an excess of thyroid hormone, hyperthyroidism results.  The only way to be certain if the thyroid gland is producing the appropriate amount of hormones is to measure their presence in the blood.

Blood Tests

Blood tests are used to measure thyroid hormone levels in the blood.  There are four types of blood tests.  Each test measures the presence of a different type of hormone.

1. The T3 test measures the amount of triiodothyronine, commonly known as T3, that is floating free in the blood and the amount attached to thyroid binding globulin, TBG.


2. The T4 test measures the amount of thyroxine, commonly known as T4, that is free floating free and the amount attached to TBG.


3. The T3 Resin Uptake Test, known as T3RU, measures the amount of TBG protein in the blood.  Under normal conditions most T3 and T4 hormones are attached to TBG proteins, not free floating.


4. The TSH test measures the amount of thyroid stimulating hormone, or TSH, in the blood.  TSH is produced by the pituitary gland, which is located in the brain.  It functions to regulate the thyroid's production and release of T3 and T4.

Normal Test Result Range

Test range values differ somewhat from one lab to another.  Laboratory test results typically have a normal range noted for each test performed.  Consult a physician with questions or concerns regarding test results

• T3 test normal range is 100 to 200 ng/dL (nanograms per deciliter)


• T4 test normal range is 4.5 to 11.2 mcg/dL (micrograms per deciliter)


• TSH test normal range is 0.4 to 4.0 mIU/L (milli-international units per liter)

Thyroid Scan

A thyroid scan uses radioactive material to measure the speed with which the thyroid absorbs iodine.  Iodine is an essential element in the production of thyroid hormones. 

The patient is given a radioactive iodine material.  After a prescribed amount of time a scanner produces an image of the thyroid detailing the amount of iodine it has absorbed.  This tells doctors if there is an iodine issue.

A thyroid scan will also show the presence of nodules, cancer or other anomalies.