Lab tests
Thyroid test results explained: TSH, T4 and T3
Thyroid reports are short but easy to misread, because the signalling hormone and the thyroid hormones usually move in opposite directions. Add your report below to see what each line is and how your value sits against the laboratory's own range.
Explain your thyroid test
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What you get
- TSH, T4, T3 and any antibody results on separate rows.
- The difference between free and total hormone results explained.
- A marker on each line your report shows as high or low.
- Questions to ask your doctor about the pattern of results.
Lines you may see on a thyroid report
- TSHThe signal from the pituitary gland that tells the thyroid how much hormone to make
- Free T4 (FT4)The main hormone made by the thyroid, measured as the part not bound to proteins
- Free T3 (FT3)The more active thyroid hormone
- Total T4 and total T3Bound and unbound hormone together
- Thyroid antibodies such as anti-TPOProteins made by the immune system that react with thyroid tissue
What this tool cannot tell you
Thyroid results are interpreted as a set and in context: pregnancy, other illnesses, some medicines and some supplements can all shift them, and ranges differ between laboratories. MedicDecode explains the lines on your report. It does not diagnose a thyroid condition or comment on thyroid medicine doses.
Common questions
How do I understand T3, T4 and TSH results?
TSH comes from the pituitary gland and rises when thyroid hormone (T4, T3) is low, falls when it is high. Doctors read the three together rather than any one alone.
What TSH level should I worry about?
Your report prints its reference range. A result outside it is interpreted with your free T4, symptoms and history, so ask your doctor what yours means.
Why does my report only show TSH?
Many laboratories measure TSH first and only add T4 or T3 when the TSH is outside its range or when the doctor asks for them.
What is the difference between free and total T4?
Most thyroid hormone in the blood is attached to proteins. Total T4 counts all of it; free T4 counts only the unattached part.
Will it tell me whether to change my thyroid tablet dose?
No. Doses are adjusted by your doctor using your results, symptoms and history. Do not change a dose because of an explanation here.
Words you may see on this report
Tap a word for its plain-English meaning, an example line and what it does not mean.
- TSH (Thyroid-Stimulating Hormone)
TSH is a hormone from the pituitary gland that tells the thyroid how much thyroid hormone to make; it is the usual first test of thyroid function.
- ALT (Alanine Aminotransferase)
ALT is an enzyme found mainly in the liver; when liver cells are irritated or damaged, more ALT leaks into the blood.
- AST (Aspartate Aminotransferase)
AST is an enzyme found in the liver, muscles, heart and other tissues; raised levels can signal stress or damage in one of these.
- Bilirubin
Bilirubin is a yellow substance made when old red blood cells break down; the liver processes it so it can leave the body.
- Creatinine
Creatinine is a waste product from normal muscle activity that the kidneys filter out, so its blood level helps show how well the kidneys work.
- CRP (C-Reactive Protein)
CRP is a protein made by the liver that rises quickly when there is inflammation or infection in the body.
- Culture and Sensitivity
A culture and sensitivity test grows germs from a sample to identify them, then checks which antibiotics can stop them.
- eGFR (Estimated Glomerular Filtration Rate)
eGFR is an estimate of how well your kidneys filter waste from your blood, calculated from a creatinine blood test plus details like age.
- Electrolytes
Electrolytes are minerals in the blood, such as sodium, potassium and chloride, that carry an electric charge and help the body work.
- ESR (Erythrocyte Sedimentation Rate)
ESR measures how fast red blood cells sink in a tube of blood over an hour; a faster rate can be a general sign of inflammation.
- Fasting Sample
A fasting sample is blood taken after you have had nothing to eat or drink except water for a set number of hours.
- Ferritin
Ferritin is a protein that stores iron; its blood level gives a good idea of how much iron the body has in reserve.
Medicines connected to this test
Their official labels mention this kind of test. Each is explained in plain English.
- Levothyroxine Sodium
a synthetic thyroid hormone (L-thyroxine, also called T4), described on the label as chemically identical to the hormone made by the human thyroid gland