A Free T4 (Free Thyroxine) test measures the unbound portion of thyroxine, the main hormone produced by your thyroid gland. Free T4 is the most useful measure of T4 hormone availability.
What This Test Measures
Free T4 (Free Thyroxine):
T4 is the primary hormone produced by the thyroid gland. Most T4 is bound to carrier proteins in the blood; only the “free” portion (about 0.03%) is available to enter cells. T4 is converted to the more active T3 in tissues throughout the body.
Reference Ranges
Normal Free T4: 0.8-1.8 ng/dL (ranges vary by laboratory)
Who Should Consider This Test
• Follow-up to abnormal TSH results
• Confirming or differentiating thyroid disorders:
– Hypothyroidism: Low Free T4 with high TSH
– Hyperthyroidism: High Free T4 with low TSH
– Secondary hypothyroidism: Low Free T4 with low/normal TSH (pituitary issue)
• Monitoring thyroid medication effectiveness
• Symptoms of thyroid dysfunction:
– Fatigue
– Weight changes
– Temperature intolerance
– Hair and skin changes
– Mood changes
Why Free T4 Instead of Total T4?
Total T4 measures both bound and free hormone. Binding protein levels can change due to pregnancy, estrogen use, liver disease, or other factors, making Total T4 misleading. Free T4 measures only the active, available hormone.
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 relative to your dose.
Related Tests to Consider
• TSH – Primary screening test (order together for complete picture)
• Free T3 – Active hormone converted from T4
• Thyroid Peroxidase Antibodies – Autoimmune thyroid evaluation
• Comprehensive Thyroid Panel – Complete evaluation
Why Choose Wittmer Rejuvenation Clinic
At $11.25, our Free T4 test is significantly less expensive than 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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