Thyroid Function Tests Flashcards
TSH can be used as a screening test for potential thyroid disease, T/F?
T
When would you measure T3 and T4?
When the TSH is abnormal
Are TSH levels high or low in hyperthyroidism?
Low - as TSH is suppressed by the high levels of T3 and T4.
With the exception of a pituitary adenoma where TSH is high.
In hypothyroidism is TSH high or low?
TSH is high in hypothyroidsim as it is trying to stimulate more thyroid hormone release.
With the exception of pituitary or hypothalamic cause of the hypothyroidism (secondary hypothyroidism). In which case the TSH level to be low.
What TSH and T3 + T4 levels would you expect in hyperthyroidism?
TSH - Low
T3 + T4 - High
What TSH and T3 + T4 levels would you expect in primary hypothyroidism?
TSH - High
T3 + T4 - Low
What TSH and T3 + T4 levels would you expect in secondary hypothyroidism?
TSH - Low
T3 + T4 - Low
What are antithyroid peroxidase (anti-TPO) antibodies?
They are antibodies against the thyroid gland itself. They are the most relevant thyroid autoantibody in autoimmune thyroid disease.
Present in Grave’s disease and Hashimoto’s thyroiditis
What are antithyroglobulin antibodies?
They are antibodies against thyroglobium, a protein produced and extensively present in the thyroid gland. Measuring them is of limited use as they can be present in normal individuals. They are are usually present in Grave’s Disease, Hashimoto’s Thyroiditis and thyroid cancer.
What are TSH receptor antibodies?
TSH Receptor Antibodies are autoantibodies that mimic TSH, bind to the TSH receptor and stimulate thyroid hormone release. They are the cause of Grave’s Disease and so will be present in this condition.
What are the different imaging methods that can be used to investigate the thyroid gland?
- Ultrasound imaging
2. Radioisotope scan
How can an ultrasound scan be used when investigating thyroid disease?
Ultrasound of the thyroid gland is useful in diagnosing thyroid nodules and distinguishing between cystic (fluid filled) and solid nodules. Ultrasound can also be used to guide biopsy of a thyroid lesion.
How can a radioisotope scan be used when investigating thyroid disease?
Radioisotope scans are used to investigate hyperthyroidism and thyroid cancers. Radioactive iodine is given orally or intravenously and travels to the thyroid where it is taken up by the cells. Iodine is normally used by thyroid cells to produce thyroid hormones. The more active the thyroid cells, the faster the radioactive iodine is taken up. A gamma camera is used to detect gamma rays emitted from the radioactive iodine. The more gamma rays that are emitted from an area the more radioactive iodine has been taken up.
What functional information does a radioisotype scan give about the thyroid gland?
- Diffuse high uptake is found in Grave’s Disease
- Focal high uptake is found in toxic multinodular goitre and adenomas
- “Cold” areas (i.e. abnormally low uptake) can indicate thyroid cancer
