A Free T3 (Free Triiodothyronine) test measures the unbound, active form of T3 in your blood. T3 is the most metabolically active thyroid hormone, regulating metabolism, energy, and body temperature.
What This Test Measures
Free T3 (Free Triiodothyronine):
T3 is the active thyroid hormone that affects nearly every cell in your body. Most T3 is bound to proteins; the “free” portion (about 0.3%) is what’s available to enter cells and exert effects. This test measures only the unbound, active portion.
Reference Ranges
Normal Free T3: 2.0-4.4 pg/mL (ranges vary by laboratory)
Who Should Consider This Test
• Those with abnormal TSH but normal Free T4
• Suspected hyperthyroidism (overactive thyroid) – T3 may rise before T4
• Symptoms persisting despite normal TSH and T4:
– Fatigue
– Weight changes
– Temperature sensitivity
– Brain fog
• Evaluation of T3 toxicosis (elevated T3 with normal T4)
• Monitoring thyroid medication (especially T3-containing medications like Cytomel or desiccated thyroid)
• Suspected thyroid hormone conversion issues (T4 to T3)
T3 vs. T4
• T4 is the main hormone produced by the thyroid gland (prohormone)
• T3 is mostly converted from T4 in tissues (the active hormone)
• T3 is 3-4 times more potent than T4
• Some individuals have difficulty converting T4 to T3
How It Works
1. Order your test online – no doctor visit required
2. Visit any Quest Diagnostics location nationwide
3. Simple blood draw takes approximately 5 minutes
4. Results delivered to your secure portal within 1-2 business days
Preparation
No fasting required. If taking thyroid medication, follow your provider’s instructions about timing.
Related Tests to Consider
• TSH – Primary thyroid screening test
• Free T4 – Main thyroid hormone output
• Reverse T3 – Inactive form of T3
• Thyroid Peroxidase Antibodies – Tests for autoimmune thyroid disease
• Comprehensive Thyroid Panel – Complete evaluation
Why Choose Wittmer Rejuvenation Clinic
At $24, our Free T3 test is competitively priced compared to typical hospital charges. We partner with Quest Diagnostics for reliable, CLIA-certified laboratory testing with convenient locations across all 50 states.
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