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Key Thyroid Function Tests
Laboratory Values and Interpretation

(Note: These are general values/averages. Lab values can vary somewhat from lab to lab. Always check to find out what the specific normal range is for the test value at YOUR lab.)

Test / Name
Normal Range
"TSH" Test -- Thyroid Stimulating Hormone / Serum thyrotropin 0.4 to 6

0.3 to 3.0 (as of 2003)
Under .4 can indicate possible hyperthyroidism. Over 6 is considered indicative of hypothyroidism. Note: the American Association of Clinical Endocrinologists has revised these guidelines as of early 2003, narrowing the range to .3 to 3.0. Many labs and practitioners are not, however, aware of these revised guidelines. (See Endos Say Normal TSH Range Now .3 to 3: Millions More at Thyroid Risk)
Total T4 / Serum thyroxine 4.5 to 12.5 Less than 4.5 can be indicative of an underfunctioning thyroid when TSH is also elevated. Over 12.5 can indicate hyperthyroidism. Low T4 with low TSH can sometimes indicate a pituitary problem.
Free T4 / Free Thyroxine - FT4 0.7 to 2.0 Less than 0.7 is considered indicative of possible hypothyroidism.
T3 / Serum triiodothyronine 80 to 220 Less than 80 can indicate hypothyroidism.

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