Lab test
Thyroid Blood Testing - Thyroid Level Test
This blood test evaluates three related measures of thyroid function: T3 uptake, T4, and the T7 index.
- Typical price
- From $39
- Results
- 1-3 business days
- Preparation
- See preparation notes below
- Sample
- Blood draw or sample collection at a local center
About this test
This blood test evaluates three related measures of thyroid function: T3 uptake, T4, and the T7 index. The thyroid gland produces hormones that set the pace of metabolism throughout the body, influencing energy, weight, temperature, and heart rate. The T3 uptake test estimates how much thyroid hormone binding capacity is available, T4 measures the main thyroid hormone thyroxine, and the T7 index combines the two to give a corrected estimate of free thyroxine. Together these results help investigate symptoms of an overactive or underactive thyroid. They are interpreted with reference ranges and the broader clinical picture.
What this test measures
- T3 Uptake An indirect measure of thyroid hormone binding capacity in the blood.
- T4 (Thyroxine) The main hormone produced by the thyroid gland.
- T7 (Free Thyroxine Index) A calculated index that corrects T4 for binding capacity.
Who this test may be right for
- Adults with fatigue, weight change, or temperature intolerance
- People with palpitations, unexplained anxiety, or tremor
- Individuals with a family history of thyroid conditions
- Those being monitored for known thyroid concerns
Before your visit
- Report thyroid medications and supplements containing biotin to the laboratory
- Follow any timing instructions provided with your order
- Tell your provider if you are pregnant, as ranges and interpretation differ
Understanding your results
The T3 uptake, T4, and T7 index are compared against reference ranges and interpreted together. A high T7 index with elevated T4 can be consistent with an overactive thyroid, while a low index may accompany an underactive thyroid. Because binding proteins, medications, and pregnancy can affect these measures, the pattern across all three is more informative than any single result. A healthcare provider should interpret the findings with your symptoms and possibly additional tests.
Order this test online
- Buy online in a few minutes - no doctor's visit needed for most tests.
- Sample collection at a patient service center near you.
- Results are typically ready within 1-3 business days.
- Secure, lab-reviewed results delivered to your account.
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Questions people ask
What is the T7 index?
The T7 index, or free thyroxine index, is calculated from T4 and T3 uptake to estimate the free, active proportion of thyroxine.
Does T3 uptake measure T3 hormone?
No. Despite the name, the T3 uptake test measures binding capacity rather than the amount of T3 hormone itself.
How do these results relate to an overactive or underactive thyroid?
An elevated T7 index can accompany an overactive thyroid and a low index an underactive one, but a healthcare provider confirms the interpretation with additional testing.
Can medication affect thyroid test results?
Yes. Thyroid medications, biotin, and other treatments can influence results, so report them to the laboratory and your provider.
What does the Thyroid Blood Testing - Thyroid Level Test measure?
This quick blood test evaluates thyroid three important thyroid levels: T3 uptake, T4, and T7, and is used to help diagnose hyperthyroidism or hypothyroidism.
Do I need to fast before this test?
Follow the lab's instructions.
How long do results take?
Most Thyroid Blood Testing - Thyroid Level Test results are released in 1-3 business days. Specialty testing can take longer.
Is this test right for me?
This page is educational and not medical advice. Talk to a licensed healthcare provider about which tests fit your situation.
LabBookings is an independent directory. We compare test details and pricing information, but we are not a laboratory and we do not perform testing or provide medical advice. Always talk to a licensed healthcare provider about your results and treatment.
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