Medical Lab Rat Teaches You, Today: Monitoring Thyroid Function.

Tests involved: TSH, T3, T4, TBG, TPOAb, TgAb, TRAb, and TSI.
Basics
The hypothalamus senses a drop in thyroid hormones, as a consequence, it releases TRH to stimulate the pituitary to release TSH, which them travels to the thyroid to induce the release of T3 and T4. T4 is the prohormone of T3 (active). T3 binds transcription factors in the body’s cells to upregulate metabolism.
DISEASE STATES:
Primary Hyperthyroidism
TSH: decreased.
T3: increased.
T4: increased.
TBG (transport protein): normal.
TRAb: reactive.
Thyroid stimulating antibody (TSI): reactive.
Typically caused by the formation of a TSH Receptor Antibody (Grave’s disease).
Secondary Hyperthyroidism
TSH: increased.
T3: increased.
T4: increased.
TBG (transport protein): normal.
Usually a pituitary benign tumor releasing TSH and overdriving the thyroid.
Primary HYPOparathyroidism
TSH: increased.
T3: decreased.
T4: decreased.
TBG: normal.
The most common cause in well fed adults is immune attack of the thyroid (Hashimoto’s disease) but could be a nutritional iodine deficiency.
Secondary HYPOthyroidism.
TSH: low to absent.
T3, T4: decreased.
The TBG binding protein is normally high in pregnancies.