Blood tests are often used to help determine thyroid function. Thyroid stimulating hormone (TSH) is often a screening tool and can be used along with serum T3 and T4 levels. If these hormones are abnormal, and further information regarding a possible cause is needed, antibody levels in the blood can be checked. Depending on the clinical situation, your doctor may look for specific antibodies such as:
- Antithyroglobulin antibodies
- Anti TPO antibodies
- TSH receptor stimulating antibodies
- If cancer is suspected, a thyroglobulin level may be ordered, and in rare circumstances, a calcitonin levels may be checked.
If there is concern about the structure of the gland, if size needs to be quantified or if there is a suspicion of cancer, imaging tests may be performed. Common modes of imaging include an ultrasound of the thyroid gland and radioiodine scanning and uptake. The ultrasound helps show size and consistency of the gland (for example, it is good at detecting cysts or calcifications within a gland), but it cannot always tell a benign gland from a cancerous gland. Ultrasounds may be done in a doctor’s office or in a hospital Radiology department.
Thyroid scans involve the use radioactively labeled form of iodine and are usually performed the Radiology department of a hospital or clinic. Since the thyroid is the only tissue in the human body that picks up iodine, the scan is very specific for finding thyroid tissue. If the thyroid is not picking up iodine normally, “spots” show up on the scan. A “cold” spot implies that the tissue is not picking up enough iodine compared to the rest of the gland. This may be seen in nonfunctioning nodules and may also be a sign of malignancy.
A “hot” spot implies that the tissues in that area is taking up more iodine than the surrounding tissue, and is overactive. This may be seen in a toxic nodule. Hot spots are rarely ever cancerous. In addition, there are comparison values to determine what normal thyroid uptake should be. A normal thyroid picks up 8%-35% of the administered dose of iodine within 24 hours. If values above or below this range is seen, it may point to underlying thyroid disease.