Thyroid results —
TSH, T3, T4
decoded simply.
Your TSH came back outside the normal range and you've been Googling hypothyroidism vs hyperthyroidism for an hour. Let's clear this up — the thyroid panel explained in plain English.
Dr. Emma Walsh, MD, MPH
Preventive Medicine, Thyroid Disorders ·
The essentials — before you read the full guide below.
TSH is the master control
TSH from the pituitary tells the thyroid how hard to work. Low TSH usually means the thyroid is overactive; high TSH means it's underactive.
Normal TSH range
0.4–4.0 mIU/L is the standard adult reference range. Below 0.4 suggests hyperthyroidism; above 4.0 suggests hypothyroidism.
T3 and T4 add context
Free T4 and Free T3 show actual hormone levels. TSH alone is usually sufficient for screening — T3/T4 are added when TSH is abnormal.
Symptoms drive treatment
Many people with mildly abnormal TSH have no symptoms and don't require immediate treatment. Results and symptoms are weighed together.
Reference Ranges
What does your number
actually mean?
Use the interactive slider below, or read the range cards for a full clinical breakdown.
Thyroid Panel (TSH, T3, T4) Reference Ranges
mIU/L (TSH)Enter your result
Drag to see what your Thyroid Panel (TSH, T3, T4) means
The Science
How the thyroid axis actually works
The thyroid gland produces hormones (T3 and T4) that regulate metabolism throughout the body. TSH is the signal from the brain's pituitary gland that tells the thyroid how much hormone to make — like a thermostat.
TSH is the thermostat signal
When T3/T4 levels drop, the pituitary releases more TSH to stimulate the thyroid. When T3/T4 are high, TSH drops to slow production. An abnormal TSH is the first detectable signal of thyroid dysfunction.
T4 converts to active T3
The thyroid mostly produces T4 (storage form). Tissues convert T4 to the active T3. Some people convert poorly despite normal T4 — which is why Free T3 is measured separately.
95% of thyroid disease is autoimmune
Hashimoto's (hypothyroid) and Graves' disease (hyperthyroid) account for the vast majority of thyroid disorders. Anti-TPO antibody testing confirms autoimmune origin.
When to Test
Signs your doctor will
order this test
These are the most common reasons a Thyroid Panel (TSH, T3, T4) test is requested — from symptoms to routine screening.
Cold intolerance & fatigue (Hypo)
Hypothyroidism slows metabolism — fatigue, cold sensitivity, weight gain, constipation, and brain fog are classic symptoms.
Hypothyroid signsHeat intolerance & anxiety (Hyper)
Hyperthyroidism speeds metabolism — heat intolerance, weight loss, rapid heartbeat, anxiety, and insomnia.
Hyperthyroid signsHair loss and dry skin
Both hypo and hyperthyroidism can cause hair thinning. Hypothyroidism also causes dry, coarse skin.
Both typesBrain fog & memory issues
Hypothyroidism commonly impairs cognitive function — difficulty concentrating, poor memory, mental slowness.
Hypothyroid signFamily history of thyroid disease
Autoimmune thyroid conditions run in families. First-degree relatives of Hashimoto's patients have 5× higher risk.
Risk factorPregnancy or planning to conceive
Thyroid disorders significantly affect fertility and pregnancy outcomes. TSH screening is recommended before conception.
Critical screeningTesting Schedule
How often should
you get tested?
Frequency depends on your current health status and your doctor's guidance.
Healthy adults
No family history, no symptoms, no medications. Every few years for general thyroid surveillance.
Risk factors present
Family history of thyroid disease, personal history of autoimmune conditions, or taking lithium or amiodarone.
On thyroid medication
Levothyroxine takes 6–8 weeks to stabilise. TSH is rechecked 6–8 weeks after each dose change.
Pregnant or trying
Thyroid requirements increase in pregnancy. TSH is monitored each trimester to adjust dose.
If Your Result Is Abnormal
If your TSH is abnormal — what next
An abnormal TSH doesn't automatically mean you need treatment. Here's the typical pathway.
Confirm with Free T4/T3
An abnormal TSH is followed by Free T4 (and sometimes Free T3) to assess actual hormone levels and determine whether treatment is needed.
First stepAnti-TPO antibody test
If hypothyroidism is confirmed, Anti-TPO antibodies determine whether it's autoimmune (Hashimoto's). Positive antibodies increase progression risk.
Autoimmune screenLevothyroxine for hypo
Overt hypothyroidism (TSH >10) is treated with levothyroxine — a synthetic T4 taken daily. Dose is titrated by TSH response every 6–8 weeks.
Standard treatmentSelenium (Hashimoto's)
Selenium supplementation (200mcg/day) has Level 2 evidence for reducing anti-TPO antibody levels in Hashimoto's thyroiditis.
Adjunct support