Free T4 / Free T3
Free T4 / Free T3 explained
Free T4 and Free T3 measure unbound thyroid hormones to help diagnose and manage thyroid disorders.
Varies by laboratory (LDT/CLIA; not FDA‑approved as a drug)Free T4 / Free T3 helps treat
• Clarifying thyroid status with TSH
• Hyperthyroidism/hypothyroidism workup
• Medication monitoring
additional medications
• Related clinical evaluation and history
• Repeat testing to confirm abnormal results
• Additional targeted labs as recommended
medication risks
• False positives/negatives leading to unnecessary anxiety or missed diagnoses
• Privacy and insurance implications depending on results
• Pre‑analytical variables (fasting, meds) can affect accuracy
side effects
• Bruising or soreness at draw site
• Lightheadedness or fainting (rare)
• Infection at puncture site (very rare)
FAQs
Q: Biotin interference?A: Yes—biotin can distort some immunoassays; hold per guidance.
Q: Fasting?
A: Not required.
Q: When to order?
A: With abnormal TSH or specific clinical scenarios.
Q: Pregnancy reference ranges?
A: Differ and should be used when applicable.
Q: Insurance?
A: Typically covered when indicated.
