Thyroid Scan Report: Uptake, Hot and Cold Nodules Explained
A thyroid scan report answers one question an ultrasound can’t: which parts of the thyroid are actively soaking up iodine. High, even uptake usually points to Graves’ disease, a single “hot” spot to an overactive nodule, and low uptake with high hormones to inflamed thyroid (thyroiditis) leaking stored hormone.
Before you start
- What it is: a tiny amount of radioactive iodine or technetium is given, then a camera photographs the neck.
- Why it’s ordered: mostly to find the cause of an overactive thyroid, or to check a nodule when TSH is low.
- Hot nodule: takes up more tracer, appears darker; can be overactive.
- Cold nodule: takes up little, appears lighter; often needs ultrasound and sometimes FNAC.
- Not for: pregnant or breastfeeding women, unless a specialist decides otherwise.
What does a thyroid uptake scan show?
Your thyroid makes hormone from iodine, so it pulls iodine out of the blood like a magnet. Give it a small, traceable dose and a gamma camera can see where the magnet is strongest. Two things appear on the report:
- The picture (scan): the shape of the gland and whether uptake is even or patchy.
- The number (uptake): the percentage of tracer the gland took in at a set time, judged against that department’s normal range.
The scan doesn’t measure hormone levels. That’s the job of the blood test explained in our TSH, T3 and T4 guide. The scan explains why the levels are what they are.
High vs low uptake: what do the patterns mean?
| Pattern on report | Most likely cause | What usually follows |
|---|---|---|
| Diffuse, evenly high uptake | Graves’ disease | Specialist plan for overactive thyroid |
| One hot nodule, rest of gland faint | Toxic (overactive) nodule | Treatment aimed at that nodule |
| Several hot and cold patches | Toxic multinodular goitre | Specialist review |
| Low uptake with high T4 | Thyroiditis or extra iodine/hormone intake | Often watchful waiting |
| Cold nodule | Non-functioning nodule | Ultrasound and possibly FNAC |
Hot nodule vs cold nodule: should I worry?
A hot nodule is working hard, sometimes too hard, causing an overactive thyroid. Hot nodules are rarely cancerous, which is why some specialists skip a biopsy for them.
A cold nodule simply isn’t making hormone. Most cold nodules are harmless too, but this is the group where cancer, when it occurs, tends to sit. So a cold nodule usually leads to a proper ultrasound with a TI-RADS grade (see our thyroid ultrasound report guide) and, if the grade and size warrant it, a needle sample read with the Bethesda system (see the FNAC report guide).
“Cold” means quiet, not dangerous. It just earns a closer look.
Why might uptake be low?
Low uptake with high hormone levels usually means the gland is leaking hormone it already made, not producing new. Thyroiditis does this: after a viral illness with a painful, tender neck, after childbirth, or with certain medicines. These episodes often settle over weeks to months, sometimes passing through an underactive phase. Antibody tests such as anti-TPO (see the anti-TPO report guide) can add to the picture.
Low uptake can also be a preparation problem. Extra iodine floods the gland so it ignores the tracer. Common sources: a CT scan with iodine contrast in the past couple of weeks, kelp or seaweed supplements, some heart and thyroid medicines, and iodine-containing antiseptics or cough products.
Tell the nuclear department this when booking
Mention any CT scan with contrast dye in recent weeks, every medicine and supplement (bring the strips and bottles), and any recent diarrhoea. Ask whether they want you to avoid iodine-rich items such as seaweed snacks or kelp tablets beforehand, and follow their list exactly. A wasted scan from hidden iodine is common and avoidable. Never stop a prescribed thyroid or heart medicine for the scan unless your doctor tells you to.
How do I prepare for the scan?
- Confirm you are not pregnant; women of childbearing age are often asked to do a pregnancy test.
- If breastfeeding, tell the department before booking; the test is usually avoided or planned with a specialist.
- Follow the fasting instruction, often nothing to eat from midnight.
- Bring all medicines and a list of recent scans.
- Remove necklaces, earrings and dentures with metal before imaging.
- Expect to return later the same day or the next day for the uptake reading.
Thyroid scan vs ultrasound: which do I need?
They answer different questions. Ultrasound shows structure: size, nodules, cysts, suspicious features. The scan shows function: which parts are active. Most nodules with a normal TSH need only ultrasound. A scan earns its place mainly when TSH is low, to decide whether a nodule is hot.
Pregnant and breastfeeding women should not have this test without specialist advice. Seek urgent care for a racing or irregular heartbeat, chest pain, severe agitation or confusion with high fever (a rare thyroid storm), or a neck swelling that grows quickly or makes breathing or swallowing hard. A tender neck with fever deserves a doctor’s review. Thyroid medicines are started, stopped and adjusted only by your doctor. The scan report describes a pattern; your endocrinologist turns it into a diagnosis.
Thyroid scan report questions
What does a thyroid uptake scan mean?
It measures how much tracer your thyroid takes up and shows where. High uptake points to an overactive gland making hormone; low uptake points to inflammation or extra iodine.
What does a cold nodule on a thyroid scan mean?
It means the nodule is not making hormone. Most are harmless, but cold nodules usually get an ultrasound and sometimes a needle test.
What is a hot nodule?
A hot nodule takes up more tracer than the surrounding gland and may cause an overactive thyroid. Hot nodules are rarely cancerous.
Thyroid scan vs ultrasound, which is better?
Neither is better; they answer different questions. Ultrasound shows structure, the scan shows function, and doctors often use both.
How do I prepare for a thyroid scan?
Usually fast from midnight, report all medicines, supplements and recent contrast scans, and avoid iodine-rich items as the department instructs.
What does low uptake with thyroiditis mean?
The inflamed gland is leaking stored hormone rather than making new, so uptake is low. Many such episodes settle over weeks to months.
Can I have a thyroid scan while breastfeeding?
Usually not without specialist advice. Tell the department before booking so they can advise or choose another approach.
Can I have a thyroid scan during pregnancy?
No, it is not done in pregnancy. Doctors use blood tests and ultrasound instead.
Does a CT scan affect a thyroid scan?
Yes. Iodine contrast from a recent CT can block uptake and spoil the result, so mention any contrast scan in the past few weeks.
Find more guides in Lab Reports Decoded.