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Thyroid

Total T3 Blood Test: What Does Triiodothyronine Tell You?

Total T3 measures the most active thyroid hormone, triiodothyronine, in your blood. This marker may provide valuable insight into your metabolic health and energy levels. Including T3 testing in your health assessment can help build a comprehensive picture of thyroid function.

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

Total T3 (Triiodothyronine): what this test 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.

Total T3 (Triiodothyronine): why this value matters

Monitoring total T3 as part of a proactive health approach may help detect thyroid imbalances early. Changes in T3 levels can sometimes precede noticeable symptoms. Your healthcare provider can use this information alongside other thyroid markers to guide personalised health recommendations.

Total T3 (Triiodothyronine): how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Which test
on its own €31,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Total T3 (Triiodothyronine): how to prepare

  1. Pause biotin

    Required

    Do you take a supplement with biotin (vitamin B8, common in hair, skin and nail supplements)? Stop it 72 hours before the draw. Biotin interferes with the measurement of these values.

  • Water is always fine. Drink as usual beforehand, it makes the draw easier.
  • Take your usual medication, unless your own doctor told you otherwise.

Total T3 (Triiodothyronine): when is testing worthwhile?

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.

Total T3 (Triiodothyronine): symptoms of a high or low value

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.

Total T3 (Triiodothyronine): lifestyle and this value

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.

Total T3 (Triiodothyronine): 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.

Whoop

Whoop Women's Health

A 54-biomarker women's health panel inspired by the WHOOP Women's Health Panel — fertility, cycle and thyroid hormones plus a complete metabolic and nutrient base.

Complete Blood Count (CBC) ALP (Alkaline Phosphatase) ALT (Alanine Aminotransferase) AST (Aspartate Aminotransferase) Albumin Total Protein Bilirubin (Total) ApoB (Apolipoprotein B) Total Cholesterol LDL Cholesterol HDL Cholesterol Triglycerides Lipoprotein(a) Urea (BUN) Creatinine eGFR (Estimated Glomerular Filtration Rate) Calcium Bicarbonate Chloride Sodium Potassium Magnesium Cortisol DHEA-S Estradiol (E2) FSH (Follicle Stimulating Hormone) LH (Luteinizing Hormone) SHBG (Sex Hormone Binding Globulin) Total Testosterone Free Testosterone TSH (Thyroid Stimulating Hormone) Glucose (Fasting) HbA1c (Glycated Hemoglobin) Insulin (Fasting) HOMA-IR CRP (C-Reactive Protein) Homocysteine Ferritin Iron (Serum) Transferrin Transferrin Saturation Vitamin D (25-OH) AMH (Anti-Müllerian Hormone) Progesterone Prolactin TPO Antibodies Free T3 (Triiodothyronine) Free T4 (Thyroxine) Leptin Vitamin B12 Folate (Folic Acid) Phosphorus Bilirubin (Direct) Bilirubin (Indirect) Cholesterol/HDL Ratio Non-HDL Cholesterol LDL/HDL Ratio
€709,-

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Medical policy
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Total T3 (Triiodothyronine)

€31,-