Thyroid Profile – 3

Clinical Significance:
TSH has a circadian rhythm, with a peak around midnight (with much variability between individuals), and a low in the afternoon; fluctuations are normal.

The change in TSH from peak to trough is approximately 72%.
Normal changes in thyroid function tests during pregnancy, total T4 and T3 steadily increase during pregnancy. The thyroid gland is normally regulated by
thyroid-stimulating hormone (TSH), also called thyrotropin, which is secreted by the pituitary. TSH stimulates the thyroid gland to produce and release
the thyroid hormones thyroxine (T4) and triiodothyronine (T3) . T4 and T3 are released from the thyroid into the bloodstream, Increased levels of free thyroid
hormones (T4 and T3) inhibit TSH secretion from the pituitary, whereas decreased levels of T4 and T3 cause an increase in TSH release from the pituitary.
Note:
1. TSH levels are subject to circadian variation, reaching peak levels between 2 – 4.a.m. and at a minimum between 6-10 pm . The variation is of the order of 50%,
hence time of the day has influence on the measured serum TSH concentrations.
2. Values <0.03 uIU/mL need to be clinically correlated due to presence of a rare TSH variant in some individuals.
Decreased TSH:Graves disease, Autonomous thyroid hormone secretion, TSH deficiency.​
Increased TSH : Primary hypothyroidism, Subclinical hypothyroidism, TSH dependent Hyperthyroidism.