Free T4 and Free T3; concerning thyroid function.

Fingerstick at home – no collection point needed
You receive a fingerstick kit with clear instructions
Easily collect a few drops of blood yourself
Return via medical mail to the lab
Free T4, also known as thyroxine, is a hormone produced by the thyroid gland. It plays a crucial role in our metabolism and energy balance.
Measuring Free T4 is useful for assessing thyroid function. It is especially relevant when experiencing symptoms of an overactive or underactive thyroid, such as unexplained weight change, fatigue, or mood swings.
Free T4 levels help in evaluating thyroid function. It provides insight into how well the thyroid gland produces and secretes hormones.
A high level of Free T4 may indicate hyperthyroidism, a condition in which the thyroid gland produces too much hormone. This can lead to symptoms such as weight loss, nervousness, and a rapid heartbeat.
A low level of Free T4 may indicate hypothyroidism, where the thyroid gland does not produce enough hormone. This can lead to symptoms such as weight gain, fatigue, and cold intolerance.
Free T3, or triiodothyronine, is another important hormone produced by the thyroid gland. It is even more active than T4 and has a strong influence on metabolism.
Testing for Free T3 is useful for a more in-depth evaluation of thyroid function, especially if symptoms or results from other thyroid function tests are contradictory or unclear.
Free T3 levels provide an accurate picture of thyroid activity and are particularly useful in diagnosing hyperthyroidism or in cases where T4 levels are normal but symptoms of a thyroid disorder persist.
High levels of Free T3 may indicate hyperthyroidism, which can result in symptoms such as increased heart rate, anxiety, and sleep problems.
Low levels of Free T3 may indicate hypothyroidism, with possible symptoms such as fatigue, depression, and a sluggish metabolism.
Answers to what people usually want to know.
After ordering we ship the collection kit to your home. You prick your fingertip, collect a few drops of blood, return it in the envelope, and receive your result digitally by email.
A small prick on your fingertip lets you collect a few drops into a tube. The instructions include step-by-step photos and video, so no guessing required.
In the included return envelope with free shipping. Just drop it in the mailbox; the lab processes your sample as soon as it arrives.
Usually 2 to 5 working days after the lab receives your sample. You get an email with a link to your digital result, including explanation per value.
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This test is included in Dutch healthcare guidelines and is regularly used for its respective indications.
Rationale for this test
Vrij T4 en vrij T3 zijn standaard schildklierhormoontesten die in Nederlandse zorgrichtlijnen worden gebruikt voor het beoordelen van de schildklierfunctie. Deze bepalingen zijn klinisch gevalideerd en worden routinematig ingezet bij verdenking op hyper- of hypothyreoïdie. De klinische betekenis van deze testen is goed onderbouwd binnen de reguliere geneeskunde.
Last reviewed on
Dutch clinical guidelines and healthcare organisations
We recommend consulting these independent sources before ordering a preventive health check.
Brochure on preventive health checks: careful choice, reliability, pros and cons, checklist.
Independent information about preventive health checks from the National Institute for Public Health and the Environment.
Reliable patient information about illnesses and complaints from Dutch GPs (NHG).
Public-facing website of the Dutch Society for Clinical Chemistry with explanations of blood tests and laboratory values.