Thyroid Scintigraphy
Thyroid scintigraphy — a thyroid scan — uses a small amount of radioactive tracer to create an image of how the gland takes up iodine or a similar substance. It shows function rather than structure.
It is used in specific situations, most often to evaluate nodules or to distinguish the causes of an overactive thyroid.
Last medically reviewed: 15 November 2025
How it works
You are given a small dose of radioactive tracer, usually by mouth or injection. A camera then images the thyroid, showing which areas take up the tracer. Active tissue appears as “hot” areas and inactive tissue as “cold” areas.
The radiation dose is very small and the test is generally safe.
When it is used
A scan can show whether a nodule is functioning (hot) or non-functioning (cold). Hot nodules are almost always benign, while cold nodules may need biopsy.
It is also used to distinguish Graves’ disease (diffuse increased uptake) from thyroiditis (low uptake) when the cause of thyrotoxicosis is unclear.
Preparation and limits
You may need to avoid iodine-rich foods and certain medications for a period beforehand, as these can affect the result. Pregnancy and breastfeeding are contraindications.
Scintigraphy complements ultrasound and blood tests rather than replacing them — the images are interpreted alongside the full clinical picture.
Frequently asked questions
Is a thyroid scan safe?
Yes — the radiation dose is very small, comparable to or less than a chest X-ray. It is not the same as therapeutic radioactive iodine.
What is a cold nodule?
A cold nodule takes up less tracer than surrounding tissue. Because a small proportion of cold nodules are cancerous, they may need biopsy.
Do I need to prepare?
Often yes — you may be asked to avoid iodine-rich foods and certain medications for a period beforehand. Follow the specific instructions given.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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