Blood Tests

TSH – best single blood test.  Measures levels of thyroid stimulating hormone and should be normal.  Measures thyroid function.

T4 and T3 – should be only measured if TSH is abnormal.  Measures level of thyroid hormones (T4 and T3) in the blood. 

Thyroglobulin – mostly performed as part of thyroid cancer follow-up.  Not useful as screening test. Your endocrinologist may order some other thyroid tests, but these are otherwise not routinely performed.

Ultrasound

Ultrasound is the best investigation for looking at thyroid, especially in the context of nodules.  Recently The American College of Radiology and The American Thyroid Association have developed a set of standard criteria (TI- RADS) for reporting of the thyroid nodules (TR1-TR5) to provide recommendations of management of these thyroid nodules. Depending on the TR classification, some of these nodules do not require any further investigation or follow-up.  Some may only require follow-up with ultrasound and some may require biopsy. 

Ultrasound guided Fine Needle Aspirate (FNA)

Ultrasound guided FNA is performed if ultrasound scan has shown thyroid nodules and one or more of these shows some suspicious features as per TI RADS criteria.  The FNA is always performed using the ultrasound so that the correct nodule and area within the nodule is targeted on the biopsy.  Blind (without ultrasound) biopsy should not be performed.

Nuclear Medicine thyroid scan

This thyroid scan uses radioactive tracer (Technetium 99mTc or radioiodine 123I) to measure how much of the tracer has been absorbed by thyroid gland.  It is usually performed if patient has hyperthyroidism (overactive thyroid) to diagnose the cause of this.  The uptake of the tracer may be uniform throughout the thyroid gland (Grave’s disease) or within one or more thyroid nodules.  Radioiodine treatment of hyperthyroidism or thyroid cancer uses different radioiodine tracer, it uses radioiodine 131I.

CT scan

This scan is not frequently used for investigating at the thyroid gland.  It is usually used if you have very large thyroid to see how much of the thyroid is behind the breast bone (retrosternal) and if it is narrowing your windpipe.

In patients with thyroid cancer it may be used to assess whether the cancer is invading into the surrounding organs.  This test is not commonly performed in these situations, as these cancers do not commonly involve surrounding structures.