Thyroxine is found in two forms in the blood. FT4 refers to the free or unbound version of the hormone that enters tissues where needed. FT4 is synthesised and secreted by the thyroid gland and plays a crucial role in metabolism. Secretion occurs as a response to TSH stimulation of the thyroid gland.
Free T4 (FT4)
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Free T4 (FT4)
Thyroxine, also known as T4, when tested can help understand how the thyroid gland is functioning when analysed alongside TSH (thyroid stimulating hormone) levels.
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Clinical Details
99% of thyroxine is predominantly bound to thyroxin binding globulin (TBG). Free T4 does not bind to transport proteins but is free in the circulation and is unbound or metabolically available. This unbound fraction, or free T4 (FT4) is a precursor to Triiodothyronine (T3).
Please refer to clinical details on TSH to review overall causes of thyroid disorders.
Tests Results
| Raised TSH, low T4 | Hypothyroidism |
| Raised TSH, normal T4 | Consistent with subclinical hypothyroidism |
| Raised TSH, raised T4 | Thyroid hormone resistance, rarely TSH tumour. |
| Low TSH, raised T3 or T4 | Hyperthyroidism |
| Low TSH, normal T3, T4 | Subclinical hyperthyroidism |
| Low TSH, low T3 and T4 | Sick euthyroid disease, or pituitary disease. |
Case Study
Delivering True Innovation
At Enfer Medical, we have integrated a cutting-edge and fully automated WASPLab® (Walk Away Specimen Processor) that has significantly enhanced our testing capabilities to ensure the highest of quality when processing patient samples.
Our Services
Service
Health & Wellness
General health and wellness testing can include a variety of tests, depending on the needs of the individual or recommendations of
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Service
Sexual Health
Regular STI screening facilitates early treatment and reduces the long-term consequences of infection.
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Service
Respiratory Health
Rapid early pathogen identification has important treatment and infection control implications. See our range of tests here.
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Service
Reproductive & Female Health
Hormonal analysis is hugely beneficial to identifying problems that can arise during the reproductive years.
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Sample Type &
Volume Required
5mL venous serum
Enfer Medical
Tests/Assays
Enfer Medical offers chemiluminescent microparticle immunoassay (CMIA) technology for the quantitative assay for Free T4 (FT4). This test is CE-IVD certified.
Patient
Request Form
For clients using the Enfer Medical Client Portal, the Enfer Medical Patient Request Form (PRF) will be generated when you have completed your “Test Request” within the portal linked below.
Please note that samples suspected of containing high risk pathogens such as Mycobacterium tuberculosis should be clearly identified on the form and packed separately from other samples.
24 hours
Results are available next working day.
7 Days a Week
This assay is available seven days a week.
Packaging
The packaging/preparation of samples for delivery to the laboratory are required to be in adherence to all national regulations for the safe transport of biological materials. HSE guidance can be reviewed HERE.
There are specific packaging instructions and labelling requirements requiring triple packaging including:
- Primary leak-proof container – tube or vial containing the sample.
- Secondary watertight container, with absorbent material, intended to protect the primary container.
- Outer container protects the secondary container.
- Patient Request forms must be placed between the secondary container and the outer shipping container.
Further information on the packaging/preparation of samples for delivery to the laboratory is contained within the Enfer Medical Laboratory User Manual which clients are provided with.
Storage & Stability
Specimens must be tested within 7 days of collection and stored at 2-8°C.
Transporting
Samples
Samples
In addition to the packaging of samples, the transport/delivery of clinical samples to the laboratory is required to be in adherence to all national regulations for the safe transport of biological materials. Enfer Medical provides a fully compliant logistics service, aligned with clients’ testing requirements.
Prompt transport of specimens:
To ensure prompt testing of samples and release of results within the published test turnaround times, samples should arrive to the laboratory by 18:00. Test turnaround time is measured from receipt of the sample at the laboratory until the time the authorised results are reported to users.
Acceptance/Rejection
of Samples
of Samples
In rare cases specimens may not be suitable for testing on arrival to the laboratory. In that case the sample will be rejected at the receipt stage and the service user will be notified immediately and an explanation as to why the sample could not be processed will be provided. Reasons why samples cannot be processed include but are not limited to:
- Samples received beyond the stability limits and/or not at the correct temperature indicated for each test.
- Incorrect sample type received.
- Leaking samples, sample not received or sample insufficient for analysis as stated below within sample requirements.
- Non-compliant samples or request forms i.e. those missing sample date information, missing sample test request and/or missing sample site/type information.
- Samples received without the necessary patient identifiers.
Clients will be provided with guidance on Sample Receipt Anomalies.
Our Services
Service
Health & Wellness
General health and wellness testing can include a variety of tests, depending on the needs of the individual or recommendations of
Find Out More
Service
Sexual Health
Regular STI screening facilitates early treatment and reduces the long-term consequences of infection.
Find Out More
Service
Respiratory Health
Rapid early pathogen identification has important treatment and infection control implications. See our range of tests here.
Find Out More
Service
Reproductive & Female Health
Hormonal analysis is hugely beneficial to identifying problems that can arise during the reproductive years.
Find Out More
Result Values:
Quantitative results for FT4 are reported in numeric value in pmol/L. Please contact us for more information on the reference ranges used at Enfer Medical.
Critical results are communicated in accordance with the Communication of critical results for patients in the community- national laboratory handbook CSP041/2019
Accessing
Your Results
Following receipt at the Laboratory, results should be available on the next working day and will be reported to the referring clinician via the Enfer Medical Client Portal or in a format agreed with clients.
Established clients can login to the portal using the link above.