Free Tetraiodothyronine (FT4) Test
1,100 Kshs | Home Collection Available
Synonyms
free thyroxine
Purpose
The Free Tetraiodothyronine (FT4) test is a blood test that measures the level of unbound (free) thyroxine in the bloodstream. FT4 is one of the main hormones produced by the thyroid gland and plays a vital role in regulating the body’s metabolism, energy production, and overall endocrine function.
Measuring FT4 helps evaluate how well the thyroid gland is functioning. It is especially useful in diagnosing thyroid disorders such as hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid). Abnormal FT4 levels can affect a wide range of bodily functions and, if left untreated, may lead to serious complications like heart issues, infertility, or metabolic disturbances.
For a full diagnostic picture, this test can be combined with other tests, including TSH (thyroid-stimulating hormone, free triiodothyronine (FT3), thyroid antibody tests, Total T4, and Total T3. Together, these tests provide a comprehensive assessment of thyroid health and help guide accurate diagnosis and treatment.
Patient Preparation
The patient should avoid taking biotin supplements at least 72 to sample collection.
Samples
1ml with a minimum volume of 0.7ml of serum or plasma collected in a Gel-barrier, red-top, or green top tube (lithium heparin). Avoid using EDTA, oxalate, or citrate plasma. Transfer the separated serum to a plastic transport tube if a red-top tube is used. Store the sample at room temperature.
Reference Range
>19 years;0.82-1.77ng/dL
Results Turnaround
Within 24 hours of receipt of samples.
Diseases / Diagnostic indicators
FT4 levels can vary based on thyroid gland activity, pituitary function, or other medical conditions. Possible Outcomes of the FT4 Test include:
- High FT4 Levels:
Elevated FT4 may indicate hyperthyroidism, where the thyroid gland produces too much hormone. It can also be seen in cases of thyroiditis, toxic multinodular goiter, or as a response to certain medications. Occasionally, high FT4 levels may result from non-thyroidal illness, especially if total hormone levels are affected by protein-binding changes.
- Low FT4 Levels:
Low FT4 levels typically suggest hypothyroidism, where the thyroid is underactive. This can occur due to Hashimoto’s thyroiditis, pituitary dysfunction, or iodine deficiency. Like high levels, low FT4 can also be associated with non-thyroidal illness, especially in critically ill patients (a condition sometimes called “euthyroid sick syndrome”).
- Normal FT4 Levels:
When FT4 is within the reference range and paired with a normal TSH level, it usually indicates normal thyroid function. If FT4 is normal but TSH is abnormal, it may signal subclinical thyroid dysfunction.
Additional testing (e.g., TSH, FT3, and thyroid antibodies) is often necessary to confirm the diagnosis and understand the underlying cause.
For more information on FT4 Testing, read this study.