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Thyroid

Total T3 Blood Test: What Does Triiodothyronine Tell You?

Total T3 measures triiodothyronine, the most metabolically active thyroid hormone. For active individuals, T3 may influence metabolic rate, energy availability, and recovery capacity. Monitoring T3 can help you and your healthcare provider optimise your training readiness.

Doctor's Assessment Included

Reference Ranges

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

Male Your group
nmol/l
Low 1.3 Normal 3.1 High
Female Your group
nmol/l
Low 1.3 Normal 3.1 High

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Check your own value

What It Measures

This test measures total triiodothyronine (T3) in your blood, including both protein-bound and free forms. T3 is produced primarily by conversion of T4 in peripheral tissues and is considered the most metabolically active thyroid hormone. It may help assess overall thyroid function.

Why It Matters

Active individuals depend on optimal metabolic function for performance. T3 levels that are too high or too low may affect energy production, recovery times, and body composition. Your healthcare provider can help determine if your T3 levels are supporting your physical goals or if adjustments are needed.

When to Test

Your healthcare provider may recommend total T3 testing when hyperthyroidism is suspected, or when TSH levels are abnormal but free T4 appears normal. It may also be useful for monitoring thyroid medication effectiveness or investigating symptoms such as unexplained weight loss, anxiety, or rapid heartbeat.

Symptoms

Low Levels

Some people with low total T3 may experience fatigue, cold sensitivity, weight gain, constipation, dry skin, or low mood. However, these symptoms can have many causes. Your healthcare provider can help determine whether low T3 is contributing to your symptoms and recommend appropriate next steps.

High Levels

Some people with elevated total T3 may experience weight loss, increased appetite, rapid or irregular heartbeat, anxiety, tremors, heat intolerance, or difficulty sleeping. The severity of symptoms may vary. Discuss elevated T3 results with your healthcare provider for personalised assessment and guidance.

Lifestyle Tips

Supporting thyroid health may include maintaining a balanced diet rich in selenium and zinc, managing stress levels, getting adequate sleep, and exercising regularly. Some people find that reducing processed foods and ensuring sufficient iodine intake may be beneficial. Always consult your healthcare provider before making significant changes.

Frequently Asked Questions

What is the difference between total T3 and free T3?
Total T3 measures both protein-bound and free T3 in your blood, while free T3 measures only the unbound, active portion. Your healthcare provider may request one or both tests depending on what clinical information is needed for your evaluation.
Can medications affect total T3 results?
Yes, certain medications including oral contraceptives, hormone replacement therapy, and some other drugs may affect total T3 levels by altering binding protein levels. Inform your healthcare provider about all medications you take so they can interpret your results accurately.
Should I fast before a total T3 test?
Fasting is generally not required for a total T3 test. However, your healthcare provider may give specific instructions regarding timing or preparation. It is best to follow any guidance provided by your testing facility.

Tests with related values

These panels measure values from the same category as this marker.

Complete Health

360 Health

Broad health panel: hormones, thyroid, vitamins, lipids, liver, kidney, and blood count.

HbA1c (Glycated Hemoglobin) TSH (Thyroid Stimulating Hormone) Triglycerides Urea (BUN) Creatinine eGFR (Estimated Glomerular Filtration Rate) Free T4 (Thyroxine) LDL Cholesterol Liver Function Test (LFT) SHBG (Sex Hormone Binding Globulin) Vitamin B12 Vitamin D (25-OH) Total Testosterone Free T3 (Triiodothyronine) Ferritin HDL Cholesterol Albumin Total Cholesterol Basic Blood Count
€346,-
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InsideTracker

A 36-biomarker performance and longevity panel inspired by InsideTracker Ultimate — covering heart, hormones, metabolism, inflammation, recovery and iron status.

SHBG (Sex Hormone Binding Globulin) TSH (Thyroid Stimulating Hormone) ALT (Alanine Aminotransferase) LDL Cholesterol GGT (Gamma-Glutamyl Transferase) Cortisol DHEA-S Estradiol (E2) Free Testosterone Total Testosterone Folate (Folic Acid) Vitamin B12 Calcium Ferritin Iron (Serum) Magnesium Magnesium (Intracellular) Potassium Progesterone Sodium Transferrin CRP (C-Reactive Protein) Glucose (Fasting) HbA1c (Glycated Hemoglobin) ApoB (Apolipoprotein B) HDL Cholesterol Total Cholesterol Albumin AST (Aspartate Aminotransferase) Vitamin D (25-OH) Insulin (Fasting) Leukocyte Differential Creatine Kinase (CK) Transferrin Saturation Triglycerides Basic Blood Count
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Whoop

A 44-biomarker comprehensive health panel inspired by WHOOP Advanced Labs — a deep look at metabolism, cardiovascular risk, hormones, liver, kidney and inflammation.

SHBG (Sex Hormone Binding Globulin) TSH (Thyroid Stimulating Hormone) ALT (Alanine Aminotransferase) LDL Cholesterol Cortisol DHEA-S Estradiol (E2) Free Testosterone FSH (Follicle Stimulating Hormone) LH (Luteinizing Hormone) Total Testosterone Bicarbonate Calcium Chloride Ferritin Iron (Serum) Magnesium Potassium Sodium Transferrin CRP (C-Reactive Protein) Homocysteine Glucose (Fasting) HbA1c (Glycated Hemoglobin) ApoB (Apolipoprotein B) HDL Cholesterol Omega-3 Index Total Cholesterol Albumin HOMA-IR ALP (Alkaline Phosphatase) AST (Aspartate Aminotransferase) Bilirubin (Total) Total Protein Urea (BUN) Creatinine Vitamin D (25-OH) eGFR (Estimated Glomerular Filtration Rate) Insulin (Fasting) Leukocyte Differential Transferrin Saturation Lipoprotein(a) Triglycerides Basic Blood Count
€499,-

Total T3 (Triiodothyronine)

€31,-