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?
A. Random serum growth hormone (GH) level
B. 24-hour urinary GH excretion
C. Serum insulin-like growth factor 1 (IGF-1) level, age- and sex-adjusted
D. GH suppression test with 75g oral glucose tolerance test
Explanation
Why Serum IGF-1 (age- and sex-adjusted) is right
The clinical presentation at B — coarse facies, prognathism, macroglossia, spade-like hands, skin tags, and bitemporal hemianopsia — is the classic phenotype of acromegaly caused by chronic GH excess from a pituitary somatotroph macroadenoma. According to the Endocrine Society 2014 guidelines, elevated IGF-1 (age- and sex-adjusted) is the BEST SCREENING TEST for acromegaly. IGF-1 is produced by the liver under GH stimulation and reflects integrated GH secretion over 24 hours, making it more reliable than a single random GH measurement. A single elevated IGF-1 is sufficient to warrant further confirmatory testing.
Why each distractor is wrong
Random serum GH level: GH is secreted in a pulsatile manner and fluctuates throughout the day. A single random GH value is unreliable for screening and cannot distinguish acromegaly from normal physiology. This is explicitly noted as inferior to IGF-1 in diagnostic algorithms.
24-hour urinary GH excretion: This test is rarely used in modern practice and is not a standard screening or diagnostic test for acromegaly. It adds no advantage over serum IGF-1 or GH suppression testing.
GH suppression test with 75g OGTT: While this is the confirmatory test (GH should suppress to <1 ng/mL or <0.4 ng/mL with newer assays after glucose load), it is NOT the initial screening test. Confirmation is performed only after IGF-1 is found to be elevated.
High-YieldNEET PG
IGF-1 (not random GH) is the single best screening test for acromegaly; GH suppression with OGTT confirms the diagnosis.
Endocrine Society 2014 Acromegaly Guidelines
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