Overview.
The thyroid panel evaluates how well your thyroid gland—the butterfly-shaped organ in your neck—is regulating your metabolism. Thyroid disorders affect 10-20% of adults but often go undiagnosed because symptoms are subtle. A complete panel includes TSH (the signal from your brain), Free T4 and T3 (the actual hormones), and antibodies that can predict autoimmune thyroid disease.
A complete thyroid panel measures TSH (thyroid-stimulating hormone from the pituitary), Free T4 (the storage hormone), Free T3 (the active hormone), and thyroid antibodies (TPO and thyroglobulin antibodies). TSH alone is often used for screening, but the full panel is needed to understand thyroid function completely.
What's included.
- TSH — normal: 0.4-4.0 mIU/L · Brain's signal to thyroid (high = hypo, low = hyper)
- Free T4 — normal: 0.8-1.8 ng/dL · Thyroid hormone storage pool
- Free T3 — normal: 2.3-4.2 pg/mL · Active thyroid hormone
- TPO Antibodies — normal: <35 IU/mL · Autoimmune marker (Hashimoto's risk)
- Thyroglobulin Antibodies — normal: <20 IU/mL · Additional autoimmune marker
Preparation.
No fasting required.
When: Best drawn in the morning for consistent results. If on thyroid medication, draw blood before taking your dose. Results typically available within 24-48 hours.
- No fasting required
- Take thyroid medication AFTER the blood draw (if on medication)
- Biotin supplements can interfere—stop 2-3 days before testing
- Morning testing recommended for consistency
When it's ordered.
- Symptoms of hypothyroidism (fatigue, weight gain, cold intolerance, constipation)
- Symptoms of hyperthyroidism (weight loss, rapid heartbeat, heat intolerance, anxiety)
- Family history of thyroid disease
- Women over 35 (higher thyroid disease prevalence)
- Post-pregnancy screening
- Monitoring thyroid medication
- Unexplained metabolic changes
Interpretation.
What normal means
Your thyroid is producing and converting hormones appropriately, and your pituitary is satisfied with thyroid output. Negative antibodies indicate low risk of autoimmune thyroid disease.
Abnormal patterns
High TSH with low Free T4 (Primary hypothyroidism)
Possible causes
- Hashimoto's thyroiditis (most common)
- Iodine deficiency
- Previous thyroid treatment
- Medications
Next steps
- TPO antibodies if not done
- Consider treatment with levothyroxine
- Retest in 6-8 weeks after starting
High TSH with normal Free T4 (Subclinical hypothyroidism)
Possible causes
- Early autoimmune thyroid disease
- Recovery from illness
Next steps
- Check TPO antibodies
- Repeat in 2-3 months
- Consider treatment if TSH >10 or symptoms present
Low TSH with high Free T4/T3 (Hyperthyroidism)
Possible causes
- Graves' disease
- Toxic nodule
- Thyroiditis
- Excess medication
Next steps
- Thyroid ultrasound
- TSI antibodies
- Consider endocrinology referral
- Uptake scan if needed
Normal TSH but low Free T3 (Poor conversion)
Possible causes
- Stress (high cortisol)
- Caloric restriction
- Selenium deficiency
- Chronic illness
Next steps
- Reverse T3 (optional)
- Address stress and nutrition
- Check selenium status
Elevated TPO antibodies with normal hormones
Possible causes
- Hashimoto's before clinical hypothyroidism
- General autoimmune tendency
Next steps
- Monitor TSH every 6-12 months
- Watch for symptoms
- Anti-inflammatory lifestyle
Cost & access.
TSH alone costs $20-40; full panel with antibodies $50-150. Most insurance covers thyroid testing when there's a clinical indication. Direct-pay options available.
FAQs.
Why is TSH the first test doctors order?
TSH is the most sensitive marker—it changes before T4 or T3 become abnormal. It's an excellent screening test, but a full panel is needed to understand the complete picture.
What are thyroid antibodies and why do they matter?
TPO and thyroglobulin antibodies indicate your immune system is attacking the thyroid. Elevated antibodies predict future hypothyroidism even when current hormone levels are normal.
Should I stop biotin before thyroid tests?
Yes. Biotin (commonly in hair/skin/nail supplements) can cause falsely abnormal thyroid results. Stop biotin 2-3 days before testing.
Why might I feel hypothyroid with 'normal' labs?
The 'normal' range is broad. Your optimal set point may be different. Also, Free T3 (the active hormone) isn't always tested. Symptoms should be considered alongside labs.