Editing Thyroid (section)

=== Thyroid biomarkers ===

* TSH
** Secreted from anterior pituitary in pulsatile fashion, following circadian rhythm
** Normal range 0.4-4.12mIU/L
** Measurement can be affected by other illness (euthyroid sick syndrome) and medications such as glucocorticoids, frusemide, anticonvulsants and metformin
* T3 and T4
** Because high proportions of both hormones are bound in systemic circulation, measurement of free T4/T3 is more useful than total levels, which can be affected by fluctuations in levels of transporter proteins
* Thyroid autoantibodies
** TPOAb (anti-TPO)
*** Most accurate and most commonly used screening test for autoimmune thyroiditis (positive in >90% of patients, as well as 80% of patients with Graves disease; false positive rate 10-15%)
** TgAb (anti-Tg)
*** 80% sensitivity for autoimmune thyroiditis and 30% sensitivity for Graves disease
*** 10-15% false positive rate
*** Presence of TgAb interferes with the use of Tg measurement for the surveillance of differentiated thyroid cancer
** TRAb (anti-TSH receptor)
*** Reserved for diagnostic confirmation of Graves disease - positive in >90% of patients with the disease
*** Hypothesised to more closely correlate with severity of Graves
* Thyroglobulin (Tg)
** Precursor protein for the active iodinated forms of thyroid hormone
** Majority stored in colloid, but a small amount escapes into systemic circulation
** Particularly elevated in patients with differentiated thyroid cancer, but it's not helpful prior to surgery. Post-operative serum Tg measurement after total thyroidectomy is among the most sensitive cancer biomarkers in existence (as long as TgAb is absent - check it at the same time).
** Sensitivity can be augmented with TSH stimulation
* Calcitonin
** Serum calcitonin is the most useful biomarker for detection and surveillance of medullary thyroid cancer
** Can be performed in patients with or at risk of MTC (MEN2 syndrome)
** Controversial whether it is a good test in the workup of a thyroid nodule

[[Category:Anatomy]]