CPT code 80438 describes a thyrotropin releasing hormone (TRH) stimulation test in which a laboratory analyst measures thyroid-stimulating hormone (TSH) in three blood samples — one pre-TRH and two post-TRH — performed over a one-hour period; service type: dynamic endocrine stimulation test; typical site of service: outpatient infusion/clinic or hospital outpatient laboratory where serial blood draws and timed hormone assays are performed.

For related coverage guidance, see recent payer policy updates: Salivary Hormone Testing, Parathyroid Hormone, Phosphorus, Calcium, and Magnesium Testing, Bone Turnover Markers Testing.