The α subunit is common to TSH, LH, FSH and hCG, while the β-subunit is specific to each hormone. The subunits are synthesised and secreted independently. The α-subunit is consistently elevated in cases of TSH secreting pituitary adenoma and its secretion is autonomous and refractory to the negative feedback of thyroid hormones.
TSH α-subunit assay is indicated for the differential diagnosis of thyroid hormone resistance and TSH-secreting pituitary adenomas (levels are normal in the former and elevated in the latter)
|Sample & container required||Serum (red top)|
|Sample volume||0.5 mL|
|Turnaround time||Up to 6 weeks|
Not currently performed in house; this is a referred test