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Thyroxine (Total)
68.00
The Total Thyroxine (T4) test measures the total amount of T4 hormone in the blood. It helps assess thyroid hormone production and supports diagnosis and monitoring of thyroid conditions.
Turnaround time
2 days
Biomarkers count
1
Same-Day Appointments
UKAS Accredited Labs
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Under 18? Patients under 18 can only be seen at GB Medlabs and Clinilabs, Monday to Friday only.
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Details about Thyroxine (Total)
What is the Thyroxine (Total) test?
The Thyroxine (Total T4) test measures the total amount of thyroxine circulating in the bloodstream, including both protein-bound and free hormone. T4 is the main hormone produced by the thyroid gland and acts as a precursor to the active hormone T3.
Most T4 in the blood is bound to proteins such as thyroxine-binding globulin, while only a small fraction is biologically active. Measuring total T4 provides an overview of thyroid hormone output but does not distinguish how much hormone is available to tissues.
This test is often used alongside TSH and other thyroid tests to evaluate thyroid function more completely.
Why do I need a Thyroxine (Total) test?
Total T4 testing helps identify whether the thyroid is producing too much or too little hormone. It is particularly useful when evaluating abnormal TSH results or monitoring known thyroid disease.
You may need this test if you experience:
- Persistent fatigue or low energy
- Weight gain or unexplained weight loss
- Cold or heat intolerance
- Hair thinning or hair loss
- Palpitations or irregular heartbeat
- Anxiety, low mood, or brain fog
- Changes in appetite
- Known thyroid disorder requiring monitoring
- Abnormal TSH or thyroid screening results
The test helps clarify whether symptoms are linked to altered thyroid hormone production.
Benefits of the test
- Measures overall thyroid hormone output
Assesses total circulating thyroxine levels. - Supports diagnosis of thyroid disorders
Helps identify underactive or overactive patterns. - Complements TSH testing
Adds hormone context to pituitary signalling. - Useful for treatment monitoring
Tracks response to thyroid medication. - Detects hormone overproduction
Helpful in suspected hyperthyroidism. - Simple blood-based testing
Requires only one blood sample. - Widely used in clinical practice
Standard thyroid assessment marker. - Supports further thyroid investigation
Guides need for free hormone or antibody tests.
Step-by-step: How we offer testing
Clinic-based testing (UK-wide)
- Choose your nearest UK clinic
- Attend your appointment
- A clinician draws a blood sample
- Sample is sent to the laboratory
- Results are issued once analysis is complete
Home or hotel visit (+£60, UK-wide)
- Book a mobile phlebotomist
- Blood sample taken at your home or hotel
- No need to attend a clinic
- Sample securely transported to the laboratory
Your results explained
Low Total T4
- Reduced thyroxine levels
- UK standard (typical): <60 nmol/L
- May indicate hypothyroidism or reduced hormone production
Normal Total T4
- Thyroxine within reference range
- UK standard (typical): ~60–140 nmol/L
- Suggests normal thyroid hormone output
High Total T4
- Elevated thyroxine levels
- UK standard (typical): >140 nmol/L
- May indicate hyperthyroidism or increased thyroid hormone production
Total T4 can be influenced by protein levels and medications; interpretation alongside TSH and Free T4 is recommended.
How It Works
Simple steps to get your results
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Book Online
Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
2
Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
3
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
Take control of your health with London Blood Tests
WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.
Frequently Asked Questions
Total T4 includes both bound and unbound hormone, while Free T4 measures only the active fraction.
Yes, some drugs can alter protein binding and affect results.
Yes, protein changes in pregnancy can raise Total T4.
It is usually interpreted alongside TSH and other thyroid tests.
Yes, hormone availability may still be altered.
Yes, especially when used with TSH.
Acute illness or stress can influence thyroid results.
Yes, thyroid disorders affect all genders.
Yes, binding proteins influence total hormone measurements.
It suggests reduced thyroid hormone production and supports further endocrine evaluation.
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