What is Free Thyroxine?
Thyroxine blood tests are typically ordered to evaluate thyroid health. Until recently, total thyroxine levels were used to diagnose thyroid disorders like hypothyroidism or hyperthyroidism, but free thyroxine levels are unaffected by protein bonds, so the test gives doctors a more accurate idea of how well the thyroid is functioning.

Thyroxine and thyroid stimulating hormone tests may be ordered in a patient has a goiter or if a woman is experiencing infertility. The free thyroxine test is not ordered as a lone blood test. Typically, doctors will order other tests to gauge thyroid or reproductive health.

Normal Value Range

• Negative Pregnancy Adult: 0.8 to 1.7 ng/dL or 10.3 to 21.9 pmol/L
• Pregnancy Trimester One: 0.8 to 1.2 ng/dL or 10.3 to 15.5 pmol/L
• Pregnancy Trimester Two: 0.6 to 1 ng/dL or 7.7 to 12.9 pmol/L
• Pregnancy Trimester Three: 0.5 to 0.8 ng/dL or 6.4 to 10.3 pmol/L

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