“
REFERENCE RANGES FOR THYROID HORMONES Thyroid Hormone Normal Range Thyroid-stimulating hormone (TSH) 0.45 to 4.5 mcIU/mL (microinternational units per milliliter) Free triiodothyronine (T3) 200 to 440 pg/dL (picograms per deciliter) Total triiodothyronine (T3) 71 to 180 ng/dL (nanograms per deciliter) Free thyroxine (T4) 0.82 to 1.77 ng/dL (nanograms per deciliter) Total thyroxine (T4) 4.5 to 12 mcg/dL (micrograms per deciliter) Thyroid peroxidase (TPO) 0 to 34 IU/mL (international units per milliliter) Most doctors request only TSH and T4 levels, following up with a T3 reading if results fall outside out of the normal ranges. Some doctors place great importance on free T3 levels right away, as it is the most active thyroid hormone. If T3 levels are low compared to T4 and TSH levels, it may signify low thyroid function even if the labs otherwise appear normal.
”
”
James B. LaValle (Your Blood Never Lies: How to Read a Blood Test for a Longer, Healthier Life)