Clinical Significance

   Thyroglobulin test may be requested after the surgical removal of thyroid gland for to check any normal and/or cancerous thyroid tissue that may have been left behind. It is often checked on a regular basis, even if negative after surgery, to make sure that the tumour has not come back or spread.

Specimen

   Serum

Stability

   Refrigerated (preferred) : 14 days

   Frozen : 90 days

   Ambient : 7 days

Reference Range

   3.5 – 77 ng/ml

Interpretation

   Small amounts of thyroglobulin are present in patients with normal thyroid function. Thyroglobulin concentrations should be undetectable or very low in all patients after a thyroidectomy (surgical removal of the thyroid) and/or after subsequent radioactive iodine treatments. If concentrations are still detectable, there may be normal or cancerous thyroid tissue remaining in the patient's body indicating the need for additional treatment. If the level of thyroglobulin is low for a few weeks or months after surgery and then begins to rise over time, it is possible the cancer has returned.

Limitation

   Specimens with thyroglobulin (Tg) concentrations greater than 250,000 ng/mL may "hook" and appear to have markedly lower levels.