If you’ve had blood work done to evaluate thyroid function, you’ve probably seen abbreviations like TSH, T4, T3, and TBG. Understanding what these lab markers mean is key to properly diagnosing and managing thyroid disorders. Here’s an in-depth guide to decoding your thyroid test results:
TSH stands for thyroid stimulating hormone. Produced by the pituitary gland, TSH regulates production and release of T4 and T3 thyroid hormones from your thyroid.
TSH levels indicate how well your thyroid is functioning:
High TSH = hypothyroidism (underactive thyroid)
Low TSH = hyperthyroidism (overactive thyroid)
TSH above the normal range signals your pituitary to increase production to try to stimulate more thyroid hormone. Low TSH means too much thyroid hormone is already circulating.
Normal TSH generally falls around 0.5-5 mU/L depending on age and testing laboratory. An abnormal TSH warrants further testing to confirm hypo/hyperthyroidism.
Thyroxine, or T4, is the main hormone produced and stored within the thyroid’s follicular cells. This accounts for 80% of the body’s thyroid hormones. T4 circulates through your bloodstream largely bound to transport proteins like thyroxine-binding globulin (TBG).
Free T4 measures the unbound portion that is active in your tissues. It indicates how much T4 is available for conversion into T3. Free T4 helps evaluate thyroid function:
Low free T4 = hypothyroidism
High free T4 = hyperthyroidism
Normal free T4 range = 0.8-1.8 ng/dL
Triiodothyronine, or T3, is the active form of thyroid hormone converted from T4. This conversion happens in tissues and organs where T3 binds to receptors to carry out thyroid hormone effects.
Like free T4, free T3 indicates thyroid function:
Low free T3 = hypothyroidism
High free T3 = hyperthyroidism
Normal free T3 range = 2.3-4.2 pg/mL
Checking both free T4 and free T3 provides a thorough assessment of available thyroid hormone levels.
This measure indicates the binding capacity of TBG thyroid hormone transport proteins. It shows uptake of T3 by blood proteins using a resin with radiolabeled T3.
T3 uptake is used to calculate the free thyroxine index (FTI) along with total T4 levels. FTI provides an estimate of unbound T4 to evaluate thyroid function.
High FTI = hyperthyroidism
Low FTI = hypothyroidism
Thyroid antibodies indicate autoimmune thyroid disease like Hashimoto’s and Graves’ disease:
TPOAb - thyroid peroxidase antibody. TPO enzyme is needed for T4/T3 production. High TPOAb confirms autoimmune hypothyroidism.
Thyroglobulin antibody - targets thyroglobulin protein needed for hormone production. Elevated in Hashimoto’s.
TSH receptor antibody - binds TSH receptors, stimulating thyroid overactivity in Graves’ disease.
Getting the Right Tests
Work with your doctor to determine which thyroid tests are right for you based on risk factors, symptoms, and goals. At our clinic, we offer an Executive Lab Package that include lab tests like TSH, free and total T4/T3, antibodies, uptake, and more. [Click Here to Get Started]
Knowing your thyroid lab results empowers you to take charge of your thyroid health. We’re here to help you interpret your tests and get the proper treatment to resolve any thyroid imbalances or autoimmune issues uncovered.