Thyroid
T4 Total (Total Thyroxine)
Thyroid
Total T4 including protein-bound fraction. Complements free T4 measurement.
VAT-exempt medical service
Total T4 (TT4) quantifies all circulating thyroxine, both the protein-bound majority and the small unbound (free) fraction. T4 is the primary hormone produced by the thyroid gland and serves as the precursor to the more active T3. While Free T4 is often considered the more clinically sensitive test, measuring Total T4 alongside other markers provides a broader picture of thyroid function, particularly when changes in binding proteins are suspected.
A Total T4 test supports the diagnosis and monitoring of thyroid conditions when used as part of a full thyroid panel. It can help detect hypothyroidism and hyperthyroidism, track treatment response, and evaluate symptoms such as fatigue, weight changes, mood disturbances, dry skin, and heart rate abnormalities. It is also relevant during pregnancy when binding protein levels naturally rise.
What a high value can mean
Elevated Total T4 suggests excess thyroid hormone production (hyperthyroidism). Causes include Graves' disease, overactive thyroid nodules, thyroiditis, and excessive thyroid medication. Pregnancy and oestrogen therapy can also elevate Total T4 by increasing binding proteins without necessarily indicating true hyperthyroidism.
What a low value can mean
Low Total T4 indicates the thyroid is not producing enough hormone (hypothyroidism). Hashimoto's thyroiditis is the most common cause. Iodine deficiency, chronic illness, malnutrition, and certain medications may also suppress T4 production. Low Total T4 should be evaluated alongside TSH and Free T4 for accurate diagnosis.
No advance preparation is required. Do not take thyroid medication until after the test. Test before 10 am for best comparability. Avoid exercise before the test. Bring valid identification. If you take a supplement containing biotin (often sold for hair and nails), pause it for two days before the test, as high doses can distort the result.
Order your test
Choose your test and pay online. Your lab referral is created straight away.
Give your sample
Visit any of our partner sampling locations. No appointment needed at most of them.
The lab analyses it
Your sample is analysed at an accredited Swedish laboratory.
Get your results
Your values appear in your account with reference ranges and an explanation of each marker.
Most clinicians consider Free T4 the more useful single marker because it measures the active, unbound hormone. However, Total T4 adds context, particularly when binding protein levels are affected by pregnancy, oestrogen use, or liver conditions.
Yes. During pregnancy, rising oestrogen levels increase thyroid-binding globulin, which raises Total T4 without necessarily indicating hyperthyroidism. Free T4 is a better measure of actual thyroid activity in pregnancy.
An abnormal Total T4 should be evaluated in context with TSH, Free T4, Free T3, and potentially thyroid antibodies. Consult your healthcare provider to determine whether further investigation or treatment is needed.