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Six-marker thyroid panel with Reverse T3 — identifies cellular-level thyroid hormone resistance missed by standard function tests.
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A six-marker advanced thyroid panel measuring TSH, Free T4, Free T3, Reverse T3 (rT3), the FT3:rT3 ratio, and TPO antibodies. Clinic appointment required.
For most people, standard thyroid markers are sufficient to detect dysfunction. But a subset of patients — particularly those with chronic illness, significant physiological stress, post-viral fatigue, or on prolonged caloric restriction — produce elevated levels of Reverse T3 (RT3). RT3 is an inactive metabolite of T4 that competes with Free T3 at cellular receptors, effectively blocking thyroid hormone action at the tissue level.
The result is a clinical picture of hypothyroidism — fatigue, brain fog, cold sensitivity, slow metabolism — despite TSH and FT4 that appear normal. This panel measures TSH, FT4, FT3, Reverse T3, TPO antibodies, and TG antibodies, giving a complete view of thyroid function, conversion efficiency, and immune status.
The FT3-to-RT3 ratio is a clinically used indicator of whether elevated RT3 is impairing thyroid action at the cellular level. Because Reverse T3 requires a venous blood draw for accurate measurement, this test must be collected at a partner clinic. Results are reviewed by a GMC-registered physician within 5 to 7 working days.
Understand what each marker measures, why it matters, and what the science says — not just a list of numbers.
Pituitary regulator of thyroid output; primary screening marker for hypo- and hyperthyroidism.
Main thyroid hormone secreted by the gland; substrate for both FT3 and Reverse T3 conversion.
Biologically active form of thyroid hormone that drives cellular energy, metabolism, and temperature regulation.
Inactive T4 metabolite that competes with FT3 at receptor sites; elevated levels can cause tissue-level hypothyroid symptoms.
Autoimmune marker present in around 95% of Hashimoto's cases; can drive elevated RT3 indirectly via inflammation.
Complementary autoimmune marker that adds diagnostic sensitivity for TPO-negative autoimmune thyroid disease.
This panel is designed for adults who want a comprehensive, evidence-based picture of their metabolic health — not a GP referral panel.
People with ongoing hypothyroid symptoms and 'normal' standard thyroid results
Those with post-viral fatigue, fibromyalgia, or chronic fatigue syndrome and thyroid concerns
Individuals on prolonged caloric restriction or with severe physiological stress
Those already on levothyroxine who still feel unwell despite normal TSH
Reverse T3 measurement requires a venous blood draw for analytical accuracy and must be collected at a partner clinic; home fingerstick collection is not suitable for this marker. Elevated RT3 is a non-specific finding that can result from acute illness, physiological stress, prolonged fasting, or certain medications in addition to chronic illness, and must be interpreted in full clinical context. The FT3-to-RT3 ratio, while used clinically, is not universally standardised and is best evaluated by a physician familiar with functional thyroid medicine. This panel does not include nutritional co-factors (ferritin, vitamin D, B12) that also affect RT3 levels; consider the Comprehensive Thyroid Health Panel if these are also needed.
From order to physician-reviewed report in as little as three working days.
Three options designed to fit your schedule, location, and preference — all producing a laboratory-standard sample.
Adults 18+ in mainland UK. Not suitable if you have had a transfusion in the last 3 months.
Order anytime; kit dispatched within 24 hours Mon–Fri.
Allow 24–48 hours for sample transit on top of lab processing time.
Adults 18+ within 20 miles of a serviced city centre.
Mon–Sun, 06:00–20:00. Next-day booking typical.
Sample reaches the lab within 24 hours of collection.
Adults 16+ with photo ID. Paediatric draws by appointment at selected sites.
Mon–Fri, with Saturday hours at most metropolitan locations.
Samples processed same-day at the receiving clinic.
Every test is processed in a UKAS ISO 15189-accredited laboratory, overseen by GMC-registered physicians, and governed by UK GDPR. No overseas processing, no offshore data.
Follow these guidelines to ensure accurate, reproducible results. Most markers are sensitive to recent food, exercise, and sleep.
Can't find your answer? Our clinical support team is available Monday to Friday, 9am–5pm.
Contact supportReverse T3 (RT3) is an inactive mirror image of Free T3. Both are produced from the same precursor hormone (T4), but while FT3 binds to thyroid receptors and drives metabolism and energy, RT3 competes for the same receptor sites without activating them. When RT3 is elevated relative to FT3, it effectively ‘blocks’ thyroid hormone action at the cellular level, creating a state of functional hypothyroidism even when blood levels of TSH and T4 appear normal. This is why some people feel profoundly hypothyroid despite being told their thyroid results are fine.
The body preferentially converts T4 to RT3 rather than FT3 in situations of physiological stress — as a protective mechanism to slow metabolism during illness, fasting, trauma, or prolonged caloric restriction. Common causes of chronically elevated RT3 include chronic illness (including post-viral syndromes), adrenal dysfunction, severe nutrient deficiencies (particularly ferritin and selenium), high cortisol states, and certain medications such as corticosteroids, beta-blockers, and amiodarone. Identifying the underlying cause is as important as identifying the elevated RT3 itself.
The FT3-to-RT3 ratio is calculated by dividing the FT3 value (in pg/mL) by the RT3 value (in ng/dL). A ratio above 20 is generally considered adequate thyroid action at the cellular level; a ratio below 20 suggests that RT3 may be impairing thyroid receptor function. This ratio is not universally standardised across laboratories, and different practitioners use different thresholds. Your Trupoint Health physician will interpret the ratio in the context of your full results and clinical presentation. The ratio is a guide, not a definitive diagnostic cut-off.
RT3 measurement requires an adequate volume of serum that is reliably obtained from a venous blood draw. Capillary fingerstick samples — while suitable for most thyroid markers — can produce haemolyse or insufficient volume that affects the analytical accuracy of RT3 assays. To ensure a reliable result, we require a clinic-based venous collection for this panel. The appointment takes approximately 10 minutes and is available at partner clinic locations across the UK.
The results from this panel can provide valuable data for a prescribing physician to consider when reviewing your treatment. Some practitioners use elevated RT3 as a rationale for trialling T3 supplementation (liothyronine) or switching from levothyroxine to a combination T4-T3 medication. However, medication adjustments must only be made by a qualified prescriber, and the appropriate treatment approach is debated within endocrinology. Please share your results with your GP or specialist; do not adjust medication independently based on these results.
Standard thyroid function tests measure TSH, and sometimes FT4. The NHS rarely measures FT3 routinely, and RT3 testing is largely absent from NHS pathways. This panel specifically targets the conversion side of thyroid physiology — how T4 is being metabolised and whether it is producing usable FT3 or being shunted to the inactive RT3 pathway. It is a specialist tool for people who have already had standard testing and have reason to investigate further, not a first-line screening test.
