What this test measures
Thyroid Panel 2 measures the three thyroid markers in their most clinically informative forms:
• Free T3 (FT3) — the biologically active triiodothyronine. • Free T4 (FT4) — the biologically active thyroxine. • TSH (3rd Generation) — the pituitary signal driving thyroid output.
This panel is unaffected by changes in carrier proteins, making it the gold-standard for situations where binding proteins are unusual (pregnancy, oestrogen pills, severe liver disease, nephrotic syndrome).
Why it matters
Indian outpatient practice increasingly uses the Free TFT as the default thyroid panel — particularly when patient cost is not the limiting factor. Compared to the Total panel, it is more reliable in:
• Pregnancy and women on combined OCPs / HRT. • Patients on antiepileptic medications, anabolic steroids, or with chronic liver disease. • Fine-tuning levothyroxine in patients who remain symptomatic despite a "normal" TSH. • Suspected central hypothyroidism (low FT4 with non-raised TSH). • Working up subclinical or early hyperthyroidism with normal FT4 but raised FT3.
For most other settings the cheaper Total panel is sufficient.
How to prepare
No fasting required. Morning sample preferred. If on levothyroxine, take it after the blood draw. Stop biotin / cosmetic supplements for 48–72 hours. Continue other medications.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Free Triiodothyronine (FT3) (pg/mL)[1] | 2.3 – 4.2 pg/mL (3.5 – 6.5 pmol/L) | Low FT3 with raised TSH = hypothyroidism. Low FT3 in acute illness = sick euthyroid syndrome. | Raised FT3 with suppressed TSH = hyperthyroidism. Isolated FT3 rise with suppressed TSH = T3 toxicosis. |
| Free Thyroxine (FT4) (ng/dL)[1] | 0.8 – 1.8 ng/dL (10 – 23 pmol/L) | Low FT4 with raised TSH = primary hypothyroidism. Low FT4 with non-raised TSH = central hypothyroidism. | Raised FT4 with suppressed TSH = primary hyperthyroidism. |
| TSH (3rd Generation) (mIU/L)[1] | 0.4 – 4.0 | Suppressed TSH = hyperthyroidism, over-replacement, or biotin interference. | Raised TSH = primary hypothyroidism. |
FT3 / FT4 / TSH — common patterns
| Pattern | TSH | FT4 | FT3 | Likely cause |
|---|---|---|---|---|
| Overt hypothyroidism | ↑ | ↓ | ↓ or normal | Hashimoto's, post-RAI / surgery |
| Subclinical hypothyroidism | ↑ (4–10) | Normal | Normal | Early or mild Hashimoto's |
| Overt hyperthyroidism | ↓ | ↑ | ↑ | Graves', toxic nodule, thyroiditis |
| T3 toxicosis | ↓ | Normal | ↑ | Early Graves' or autonomous nodule |
| Central hypothyroidism | ↓ or normal | ↓ | ↓ | Pituitary disease — image pituitary |
| Sick euthyroid | ↓ or normal | ↓ or normal | ↓ first | Acute illness — re-check on recovery |
Frequently asked questions
When is Panel 2 (Free TFT) preferred over Panel 1 (Total TFT)?
In pregnancy, on oestrogen pills / HRT, in severe liver or kidney disease, on antiepileptics, and to fine-tune levothyroxine in patients with persistent symptoms despite a "normal" TSH. For most other settings, the cheaper Total panel is fine.
Should I take my thyroid medicine on the test day?
Yes, but take it after the blood draw. Taking it 1–2 hours before can transiently raise FT4 and cause misinterpretation.
Do I need to fast?
No. A morning sample is preferred for consistency.
How often is this panel repeated?
Stable on therapy: every 6–12 months. During dose changes: every 6–8 weeks. In pregnancy: at each trimester.
My TSH is normal but FT4 is low — what does this mean?
This pattern (low FT4 with non-raised TSH) suggests central hypothyroidism — a pituitary or hypothalamic problem. Workup includes pituitary imaging and a full pituitary hormone panel.
Will biotin affect this panel?
Yes — high-dose biotin in hair-skin-nail supplements interferes with all three assays, classically giving falsely high FT3/FT4 with falsely low TSH. Stop 48–72 hours before.
Why is this called "3rd generation TSH"?
Third-generation assays measure down to 0.01 mIU/L, allowing distinction between mildly suppressed and completely suppressed TSH — important in managing hyperthyroidism and over-replacement.
Related Hormones / Endocrine tests
Tests commonly ordered alongside Thyroid Panel-2 FT3, FT4, TSH-3Rd Gen, or that help interpret an unexpected result.
Sources & references
- American Thyroid Association — Thyroid Function Tests · accessed 2026-05-30T00:00:00.000Z
- Endocrine Society Clinical Practice Guidelines · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Thyroid Tests · accessed 2026-05-30T00:00:00.000Z
- Indian Thyroid Society — Consensus · accessed 2026-05-30T00:00:00.000Z
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