How to Read Your Thyroid Report: TSH, T3, T4 and What They Mean
Thyroid disorders are among the most common hormonal conditions in India - affecting an estimated 42 million people. Women are 5-8 times more likely to develop thyroid disease than men. Yet the report that comes back from a thyroid function test (TFT) is often confusing: numbers in units most people have never heard of, values that seem fine but still cause symptoms, and multiple tests that need to be read together to make sense.
This guide walks through every component of a thyroid report, what each value means, and how to interpret the overall picture.
What Does the Thyroid Do?
The thyroid gland, located in your neck, produces two main hormones:
- T4 (thyroxine) - the storage form, converted to T3 in tissues
- T3 (triiodothyronine) - the active form that acts on cells
These hormones regulate metabolism, heart rate, body temperature, energy levels, mood, gut motility, and much more. An underactive thyroid (hypothyroidism) slows everything down; an overactive thyroid (hyperthyroidism) speeds everything up.
The pituitary gland in the brain controls thyroid output by releasing TSH (Thyroid Stimulating Hormone) - when thyroid hormone is low, TSH rises to push the thyroid to produce more.
The Tests on Your Thyroid Report
TSH - The First-Line Test
What it is: The most important value on any thyroid report. TSH is the brain's signal to the thyroid.
| TSH Level | Interpretation |
|---|---|
| Below 0.4 mIU/L | Suppressed - hyperthyroidism or overtreatment |
| 0.4 - 4.0 mIU/L | Normal |
| 4.0 - 10.0 mIU/L | Mildly elevated - subclinical hypothyroidism |
| Above 10.0 mIU/L | Clearly elevated - overt hypothyroidism |
Read the inverse: High TSH means the pituitary is working hard to push the thyroid - the thyroid is underperforming. Low TSH means the brain has backed off because the thyroid is producing too much.
Indian note: India has high rates of hypothyroidism, and subclinical hypothyroidism (TSH 4-10 with normal T4) is extremely common. Whether to treat subclinical hypothyroidism is a clinical decision - many doctors treat if TSH is above 5-6 mIU/L or if symptoms are present.
Free T4 (FT4)
What it is: The circulating level of T4 (thyroxine) not bound to protein - the "available" portion.
Normal range: 0.8 - 1.8 ng/dL
How to read it alongside TSH:
| TSH | Free T4 | Interpretation |
|---|---|---|
| High | Low | Overt hypothyroidism - needs treatment |
| High | Normal | Subclinical hypothyroidism - monitor or treat |
| Low | High | Overt hyperthyroidism - needs treatment |
| Low | Normal | Subclinical hyperthyroidism - monitor |
| Normal | Normal | Euthyroid (normal thyroid function) |
Free T3 (FT3)
What it is: The active form of thyroid hormone. Usually ordered when TSH and T4 are abnormal, or when hyperthyroidism is suspected.
Normal range: 2.3 - 4.2 pg/mL
FT3 is elevated in hyperthyroidism and suppressed in severe hypothyroidism. It is less useful as a standalone test and is best interpreted alongside TSH and FT4.
Anti-TPO Antibodies (TPO Ab)
What it is: Antibodies against thyroid peroxidase - an enzyme in the thyroid. Their presence indicates autoimmune attack on the thyroid.
Normal: Below 34 IU/mL (ranges vary by lab)
What high Anti-TPO means:
- In combination with high TSH: confirms Hashimoto's thyroiditis - the most common cause of hypothyroidism in India
- With normal TSH: predicts higher future risk of developing hypothyroidism - worth monitoring annually
- With low TSH: may indicate Graves' disease (autoimmune hyperthyroidism)
Anti-Tg Antibodies (Thyroglobulin Antibodies)
What it is: Antibodies against thyroglobulin - the protein that stores thyroid hormone.
Normal: Below 115 IU/mL
Less specific than Anti-TPO alone; most meaningful when ordered together with Anti-TPO. Relevant in follow-up of treated thyroid cancer.
Symptoms That Don't Match Your Numbers
This is the most common source of frustration with thyroid reports. Your TSH is "normal" at 3.5 but you feel exhausted and gaining weight. What gives?
A few possibilities:
- TSH is in the upper half of normal - some people feel best when TSH is between 1.0-2.0 mIU/L, and feel symptoms even at "normal" levels above 3.0
- You have autoimmune thyroid disease (positive antibodies) even with normal hormone levels - the immune attack itself may cause fatigue
- Thyroid is not the cause - other conditions (iron deficiency, B12 deficiency, vitamin D deficiency, sleep apnoea) cause nearly identical symptoms
- Your T4 is not converting efficiently to T3 in tissues - total T4 and T3 may not reflect what your cells are actually receiving
If your symptoms persist with a "normal" TSH, ask your doctor about testing Free T3, Anti-TPO antibodies, iron, B12, and vitamin D before assuming the thyroid is fine.
How Often Should You Test?
| Situation | Testing Frequency |
|---|---|
| Normal TSH, no symptoms | Every 3 years (or per annual checkup) |
| Positive Anti-TPO, normal TSH | Annually |
| On thyroid medication | Every 6 weeks after dose change; then every 6 months when stable |
| Pregnancy (thyroid disease history) | Every trimester |
| Subclinical hypothyroidism under observation | Every 6 months |
Must Read
- Thyroid Test TSH T3 T4 Explained - A deep dive into each thyroid hormone and what abnormal levels mean for symptoms and treatment
- High TSH with Normal T3/T4: Subclinical Hypothyroidism Explained - The borderline grey zone that many Indians find themselves in - what it means and what to do
Try ReportSense on your own report. ReportSense will read your full thyroid panel, explain the TSH, T4, T3, and antibody results together, and generate specific questions to ask your doctor - tailored to your exact results. Try it free at reportsense.in.
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