Thyroid Function Tests: TSH, T3, T4 — What Your Results Mean

By Dashvanth Healthcare Medical Team · Reviewed by our specialists · East Delhi

Why Thyroid Testing Matters

Thyroid disorders affect 1 in 10 Indians — women are 5–8× more likely to be affected. Hypothyroidism (underactive) and hyperthyroidism (overactive) have vastly different symptoms but both significantly impact quality of life and — if untreated — can cause serious cardiac, bone, and metabolic problems.

The Key Tests

TSH (Thyroid Stimulating Hormone) — the MOST IMPORTANT screening test

• Produced by pituitary gland to stimulate thyroid
• Normal: 0.4 – 4.0 mIU/L (laboratory-specific ranges vary)
• High TSH → pituitary working harder → thyroid underactive → HYPOTHYROIDISM
• Low TSH → pituitary suppressed → thyroid overactive → HYPERTHYROIDISM
• TSH alone is sufficient to screen for thyroid disease in most cases

Free T4 (FT4)

• The main hormone secreted by the thyroid
• Normal: 12–22 pmol/L
• Confirmed LOW FT4 + HIGH TSH = Primary hypothyroidism
• Confirmed HIGH FT4 + LOW TSH = Hyperthyroidism

Free T3 (FT3)

• Active form of thyroid hormone (T4 converts to T3 in tissues)
• Less useful for routine screening; helpful for T3 toxicosis and monitoring hyperthyroid treatment

Thyroid Antibodies

• Anti-TPO antibodies: marker of Hashimoto's thyroiditis (commonest cause of hypothyroidism)
• TSH receptor antibodies (TRAb): Graves' disease (commonest cause of hyperthyroidism)