Total tetraiodothyronine (T4) Test
1,100 Kshs | Home Collection Available
Synonyms
T4, Total tetraiodothyronine
Purpose
The Total T4 Test is a blood test that measures the total amount of tetraiodothyronine (T4), a key hormone produced by the thyroid gland. T4 plays a vital role in regulating metabolism, growth, and overall energy levels in the body.
This test helps evaluate thyroid function and diagnose thyroid disorders, such as hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid). Since T4 circulates in both bound (to proteins) and free forms, the total T4 level gives an overview of overall hormone availability.
To gain a complete understanding of thyroid function, doctors often order the following tests along with Total T4, TSH, Free T4, Free or Total T3 (Triiodothyronine), Thyroid Antibody Tests, and Thyroxine-binding globulin (TBG). Together, these tests provide a more accurate diagnosis and help monitor treatment for thyroid conditions.
Patient Preparation
The patient should avoid taking biotin supplements at least 72 to sample collection.
Samples
1ml(adult),0.8(pediatric) with a minimum volume of 0.7(adult), 0.3(pediatric) ml 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
4.5-12.0 ug/dL
Results Turnaround
Within 24 hours of receipt of samples.
Diseases / Diagnostic indicators
The Total T4 Test helps detect and monitor various conditions that affect thyroid hormone levels and metabolism. Here are some possible outcomes of the test.
- Elevated T4 levels may indicate:
- Hyperthyroidism: an overactive thyroid gland.
- Neonatal hyperthyroxinemia: naturally higher levels in newborns.
- Hepatitis or liver disease may interfere with hormone metabolism.
- Primary biliary cirrhosis: a liver condition linked with altered hormone-binding proteins.
2. Reduced T4 levels may suggest:
- Hypothyroidism: underactive thyroid function.
- Liver disease or systemic illness which can reduce protein production and hormone transport.
- Nephrotic syndrome: loss of proteins through urine can lower the bound T4.
- Acromegaly: a hormonal disorder that may alter thyroid function.
In some cases, abnormal T4 levels might not directly reflect thyroid dysfunction but rather a secondary effect of other health issues or changes in protein-binding capacity. That’s why T4 results are often interpreted alongside TSH, Free T4, and clinical symptoms for accurate diagnosis.