Thyroid
T3 and T4: Normal Ranges and Reading Them With TSH
T3 and T4 are the hormones the thyroid gland actually produces, while TSH is the pituitary's instruction to make more. A thyroid report is read as that conversation, not as three separate numbers — which is why TSH and T4 moving in opposite directions is the common, expected pattern.
Normal T3 & T4 range
What a high T3 & T4 means
Raised T3 or T4 with a low TSH suggests an overactive thyroid, which can cause weight loss, a fast or irregular heartbeat, heat intolerance, tremor and anxiety.
Common causes:
- Overactive thyroid (hyperthyroidism)
- Thyroid inflammation
- Too high a dose of thyroid medication
- Some iodine-containing medicines and supplements
What a low T3 & T4 means
Low T4 with a high TSH points to an underactive thyroid — tiredness, weight gain, feeling cold, dry skin, constipation and low mood are typical. In pregnancy thyroid results are read against different targets, which is one reason not to interpret them alone.
Food & lifestyle that help
Favour
- A balanced diet with adequate iodine — iodised salt is the usual source in India
- Protein, whole grains and vegetables
- Selenium and zinc from a varied diet: nuts, seeds, dal, fish or egg where eaten
Limit
- Iodine supplements taken without advice
- Very restrictive diets while a thyroid problem is being assessed
- Taking thyroid medicine with tea, coffee, calcium or iron, which affects absorption
When to see a doctor
See a doctor to interpret any abnormal thyroid result, and never adjust a thyroid medicine dose on your own — the dose is set from the whole picture, not one value. Get advice promptly if you are pregnant or planning to be, or if you have palpitations, a swelling in the neck, or marked weight change.
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Make my free plan →Frequently asked questions
What is the difference between total and free T4?
Total T4 includes hormone bound to carrier proteins; free T4 measures only the unbound part that tissues can use. Pregnancy and certain medicines change the carrier proteins, so free values are often the more reliable reading.
Why is my TSH abnormal when T3 and T4 are normal?
That pattern — often called subclinical — means the pituitary is working harder to keep the hormones in range. Whether it needs treatment depends on how far TSH has moved, your symptoms, antibodies and whether you are pregnant. It is a conversation to have with a doctor.
Do I need to fast for a thyroid test?
Usually not, though labs often prefer a morning sample because TSH varies across the day. If you take thyroid medicine, ask whether to take it before or after the test — practice varies, and consistency between tests matters more than the rule you follow.