Acromegaly

A 48-year-old man presents to the endocrinology clinic with progressive facial changes over the past 8 years. On examination, he has frontal bossing, enlarged nose and lips, and the feature marked **C** in the diagram (mandibular prognathism) with malocclusion and dental spacing. His serum IGF-1 is markedly elevated at 680 ng/mL (normal: 90–235 ng/mL for his age). An oral glucose tolerance test shows GH remains at 2.8 ng/mL after 2 hours of 75 g glucose load. Pituitary MRI reveals a 1.8 cm sellar mass with suprasellar extension. Which of the following best explains the pathophysiology underlying the mandibular changes marked **C**?

A 45-year-old man presents with progressive enlargement of hands and feet (shoe size increased 4 sizes), deepening voice, coarsening of facial features, and daytime somnolence. Examination reveals the clinical phenotype shown at **B** in the diagram: coarsened facies with frontal bossing, prognathism, macroglossia, spade-like hands with sausage-shaped fingers, thickened skin with skin tags, and bitemporal hemianopsia on visual field testing. Recent fasting glucose is 145 mg/dL. Which of the following is the BEST INITIAL SCREENING TEST to confirm the diagnosis in this patient?