Test Background 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.
Clinical Indications 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) Instances of unexplained hyperthyroidism
Reference Range See report
Sample Required Serum (red top)
Sample Volume 0.5 mL
Turnaround Time Up to 6 weeks
Notes Not currently performed in house; this is a referred test