In this post we shall discuss about Thyroid Function Tests. A routine laboratory thyroid profile includes:
Thyroid profile/Thyroid Function Tests includes
1. Thyroid stimulating hormone
2. T4 binding ratio
3. Free T4 index
4. Serum T4
5. Resin T3 uptake
Thyroid Stimulating Hormone (TSH)
It is secreted from anterior pituitary and has negative feedback with circulating T4 and T3. It is the single best test for diagnosing primary hypothyroidism and hyperthyroidism. In primary hypothyroidism, serum TSH is increased and in hyperthyroidism condition it is decreased.
T4 binding ratio
The resin T3 uptake is converted to T4 binding ratio by dividing the measured resin T3 uptake by reference serum mean resin T3 uptake which is 30%. The resin T3 uptake and to T4 binding ratio are low and high in hypothyroidism and hyperthyroidism, respectively.
Free T4 index
It represents a calculated free T4 hormone concentration. It is calculated by multiplying total serum T4 by T4 binding ratio. The free T4 index is low and high in hypothyroidism and hyperthyroidism.
Serum T4
Measured total serum T4 reflects hormone which both binds to thyroid-binding globulin and free hormone. The normal range of serum T4 is 5–11.5 μg/DL. Hence, changes in either free hormone level or concentration in thyroid-binding globulin will alter total serum T4 but not affect free hormone level. Therefore, increased secretion of thyroid-binding globulin increases total serum T4 whereas decrease in TBG lowers total serum T4.
Resin T3 Uptake
It reflects the thyroid-binding globulin concentration and is reported as percentage, i.e. 25 to 35%. A present amount of radioactive T3 is added to patient’s sample of serum. Radioactive T3 binds to all liable binding sites on thyroid-binding globulin and left over is bound to resin and is measured.
Did you know???
Thyroid plays a major role in the metabolism, growth and development of the human body. A minor defect can cause ‘n’ number of diseases and abnormalities
