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Thyroid

Free T3 (Triiodothyronine) Test

Free T3 is considered the most active thyroid hormone and may influence your overall metabolism, energy levels, and wellbeing. Healthcare providers often view it as an important indicator of how effectively your body is utilising thyroid hormones.

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
pmol/l
Low 3.1 Normal 6.8 High
Female Your group
pmol/l
Low 3.1 Normal 6.8 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

Free T3 (Triiodothyronine): what this test measures

This test measures the unbound, active form of triiodothyronine (T3) circulating in your blood. Free T3 is believed to be the primary hormone that interacts with cells to influence metabolic rate. It may represent a small but functionally important fraction of total T3.

Free T3 (Triiodothyronine): why this value matters

Free T3 may provide insight into your body's ability to convert thyroid hormones into their active form. Some healthcare providers consider it an essential marker for understanding metabolic health and identifying subtle thyroid imbalances early.

Free T3 (Triiodothyronine): when is testing worthwhile?

Some people may consider testing Free T3 when experiencing unexplained fatigue, weight changes, or temperature sensitivity. It is often recommended alongside TSH and Free T4 when thyroid dysfunction is suspected. Your healthcare provider can advise on appropriate testing frequency.

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

Low Levels

Some people with low Free T3 levels may experience fatigue, weight gain, cold intolerance, dry skin, or difficulty concentrating. Low levels might also be associated with constipation, muscle weakness, and low mood. Consult your healthcare provider for proper evaluation.

High Levels

Some people with elevated Free T3 levels may experience rapid heartbeat, anxiety, unintended weight loss, tremors, or excessive sweating. High levels might also be associated with difficulty sleeping and irritability. Your healthcare provider can help determine the underlying cause.

Free T3 (Triiodothyronine): what to do about an abnormal value

Male

If Low

Low Free T3 may indicate hypothyroidism or conversion issues. Consider selenium supplementation and thyroid optimization.

If High

High Free T3 may indicate hyperthyroidism. Consult with an endocrinologist for proper evaluation and treatment.

Female

If Low

Low Free T3 may indicate hypothyroidism or conversion issues. Consider selenium supplementation and thyroid optimization.

If High

High Free T3 may indicate hyperthyroidism. Consult with an endocrinologist for proper evaluation and treatment.

Free T3 (Triiodothyronine): lifestyle and this value

Some people may support thyroid health by ensuring adequate selenium and zinc intake, managing stress levels, and maintaining regular sleep patterns. Avoiding extreme dieting might also help support healthy T3 conversion. Always discuss lifestyle changes with your healthcare provider.

Free T3 (Triiodothyronine): frequently asked questions

What is the difference between Free T3 and Total T3?
Free T3 measures only the unbound, active hormone available to your cells, while Total T3 includes both bound and unbound forms. Many healthcare providers consider Free T3 a more accurate reflection of thyroid function at the tissue level.
Can stress affect my Free T3 levels?
Some research suggests that chronic stress may reduce the conversion of T4 to T3, potentially lowering Free T3 levels. This is sometimes referred to as a protective mechanism. Your healthcare provider can help interpret your results in context.
Should I fast before a Free T3 test?
Fasting is generally not required for a Free T3 test, though some providers may recommend morning testing for consistency. It is advisable to follow any specific instructions from your healthcare provider regarding preparation.

Test Products

This marker is included in the following test panels.

Whoop

Whoop Performance Health

A 50-biomarker performance panel inspired by the WHOOP Performance Health Panel — recovery, blood production, thyroid, hormones, iron and nutrient status for people who train.

Complete Blood Count (CBC) Leukocyte Differential 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) IGF-1 (Insulin-like Growth Factor) Creatine Kinase (CK) Reticulocytes Free T3 (Triiodothyronine) Free T4 (Thyroxine) Vitamin B12 Folate (Folic Acid)
€689,-
Whoop

Whoop Metabolic Health

A 51-biomarker metabolic panel inspired by the WHOOP Metabolic Health Panel — blood sugar regulation, insulin, thyroid, liver and the mineral cofactors behind your metabolism.

Complete Blood Count (CBC) Leukocyte Differential 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) Leptin Zinc Selenium Iodine Copper Free T3 (Triiodothyronine) Free T4 (Thyroxine) GGT (Gamma-Glutamyl Transferase)
€799,-
Whoop

Whoop Women's Health

A 53-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) Leukocyte Differential 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
€709,-

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Medical standards

Dr. Naimi oversees the medical standards behind our content and assessments.

Medical policy
CIBG Ministerie van Volksgezondheid,
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Free T3 (Triiodothyronine)

€30,-