The FT3:FT4 ratio is a calculated measure sometimes used to help assess thyroid hormone activity by comparing free triiodothyronine (FT3) to free thyroxine (FT4). Free T3 and FreeT4 are measured when evaluating suspected thyroid dysfunction, particularly hyperthyroidism, where T3 may rise disproportionately to T4. The FT3:FT4 ratio can therefore support clinical interpretation of thyroid hormone patterns alongside TSH and other thyroid tests.
FT3:FT4 Ratio (serum)
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Clinical Details FT3:FT4 Ratio (serum)
High FT3:FT4 Ratio
A high ratio suggests that FT3 is elevated relative to FT4.
In Hyperthyroidism, T3 may rise more markedly than T4, producing a pattern sometimes called “T3toxicosis.”
Therefore, a high FT3:FT4 ratio can indicate more active or T3dominant hyperthyroidism, helping differentiate cases where excess T3 production is driving symptoms.
Low FT3:FT4 Ratio
A low ratio suggests relatively lower FT3 compared with FT4.
T3 measurement is not routinely assessed and T4 and TSH are primary markers for hypothyroidism.
A low ratio may therefore reflect reduced peripheral conversion of T4 to T3, which can occur in nonthyroidal illness or hypothyroidism, but must be interpreted with TSH and clinical findings.
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Sample Type
Volume Required
Venous serum
Enfer Medical
Result Values
Quantitative results for FT3:FT4 Ratio are reported in numeric ratio. Please contact us for more information on the reference ranges used at Enfer Medical.
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 6 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 FT3:FT4 Ratio are reported in numeric ratio. Please contact us for more information on the reference ranges used at Enfer Medical.
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.