Free T3 · low result
What does a low Free T3 mean?
Short answer
Low Free T3 is less specific than a low Free T4. It occurs in hypothyroidism, but also very commonly during illness, fasting or calorie restriction, when the body slows conversion of T4 to T3 — a normal adaptation, not a thyroid disease. Some medications (beta-blockers, glucocorticoids, amiodarone) lower it too. It is interpreted with TSH and Free T4.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
What is the normal range for Free T3?
- age 18+: 2.00 – 4.40 pg/mL
Full reference table, citations and testing options: Free T3 biomarker page.
What are the common causes of low Free T3?
- Non-thyroidal illness, fasting, very low-calorie dieting
- Hypothyroidism (usually with a high TSH and low Free T4)
- Medications: glucocorticoids, propranolol, amiodarone, some contrast agents
- Older age (mild decline is normal)
What symptoms go with low Free T3?
- Often none from the low T3 itself
- Fatigue, cold intolerance if hypothyroid
What do clinicians usually check next?
- Interpret with TSH and Free T4 — an isolated low Free T3 with both normal rarely needs treatment
- Retest when well and eating normally
- Review medications
Follow-up tests available at TestWell: TSH (Thyroid Stimulating Hormone) ($26.99), TSH + Free T4 ($27.99), Free T4 (Thyroxine) ($23.99), T3 Uptake ($22.99).
How do you recheck Free T3?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| Essential Thyroid Panel | Panel · 3 tests | $79.99 | No | 1–3 business days |
| Complete Thyroid Panel | Panel · 4 tests | $109.99 | No | 3–7 business days |
| Advanced Thyroid Panel | Panel · 7 tests | $129.99 | No | 3–5 business days |
| Free T3 (Triiodothyronine) | Test | $30.99 | No | 1–3 business days |
Common questions
My Free T3 is low but everything else is normal. Do I need T3 medication?
Usually not. Isolated low Free T3 most often reflects illness, dieting or medications; guidelines don't support treating it in isolation. Discuss with your clinician.
Sources
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.