T4 (Total)
Total thyroxine (T4) measures all T4 in blood — both the free, active fraction and the larger fraction bound to carrier proteins. T4 is the main thyroid hormone produced by the thyroid gland; the body converts it to T3 as needed.
Why it matters: Total T4 can shift when binding-protein levels change (during pregnancy or with certain medications) without an actual change in thyroid function. For specifically evaluating thyroid status, free T4 is generally preferred.
May increase with:
May decrease with:
What is T4 (Total)?
Total thyroxine (T4) measures all T4 in blood — both the free, active fraction and the larger fraction bound to carrier proteins. T4 is the main thyroid hormone produced by the thyroid gland; the body converts it to T3 as needed.
What might a high or low T4 (Total) mean?
Total T4 can shift when binding-protein levels change (during pregnancy or with certain medications) without an actual change in thyroid function. For specifically evaluating thyroid status, free T4 is generally preferred.
What is the typical reference range for T4 (Total)?
The general-population reference range shown here is 66 – 181 nmol/L. Reference ranges describe the general population and are not a personal target — discuss your results with your physician.
What can affect T4 (Total)?
It may be higher with: Hyperthyroidism, Pregnancy, Estrogen, Thyroid hormone replacement. It may be lower with: Hypothyroidism, Chronic illness, Malnutrition.
Track your T4 (Total) over time
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