A 34-year-old man has enlargement of hands and feet, frontal bossing, and a jaw that no longer fits his dentures. Random growth hormone is 8 ng/mL and IGF-1 is elevated above age-matched norms. MRI shows a 9 mm pituitary macroadenoma. Which test definitively confirms acromegaly?

• A Loss of circadian growth hormone rhythm on serial daytime sampling
• B Growth hormone rise above 10 ng/mL after TRH stimulation
• C Elevated IGF-binding protein 3 with normal growth hormone nadir on OGTT
• D Failure to suppress growth hormone below 1 ng/mL during a 75 g oral glucose tolerance test ✓

Explanation

Acromegaly is confirmed when growth hormone fails to suppress below 1 ng/mL (using modern ultrasensitive assays) during an oral glucose load, because glucose normally suppresses GH in healthy subjects while GH-secreting adenomas show paradoxical non-suppression or a paradoxical rise. D single random GH level is unreliable given pulsatile secretion. IGFBP-3 supports but does not confirm the diagnosis, and TRH stimulation testing is obsolete for routine confirmation.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.