The answer is D. A serum insulin-like growth factor 1 (IGF-1) level
Screen for acromegaly with a serum IGF-1. Growth hormone is secreted in pulses, so a single random GH level is uninterpretable — a normal value can occur between pulses in a patient with florid disease, and a high value can occur in a healthy person. IGF-1 is the mediator of nearly every clinical effect of growth hormone, it is produced by the liver in proportion to GH exposure, and its long half-life integrates secretion over days, which is exactly what makes it the right screening test. A normal age- and sex-matched IGF-1 essentially excludes the diagnosis.
The order of testing is the whole question, and boards test the order relentlessly: IGF-1 first → oral glucose tolerance test to confirm → pituitary MRI to localize. If IGF-1 is elevated or equivocal, confirm with an oral glucose load: failure of growth hormone to suppress below 1 mcg/L is diagnostic, because glucose normally shuts GH off. Only after biochemical confirmation do you image, and imaging is for localization, never for diagnosis — incidental pituitary lesions are common enough that an MRI-first strategy will mislead you.
The clinical picture here is classic. More than 95% of cases are a pituitary somatotroph adenoma. The distinction from gigantism is purely timing: excess before epiphyseal fusion makes a child tall; excess after fusion can only widen and thicken bone, which is why an adult reports rings and shoes rather than height. Almost every finding is a soft-tissue consequence — the carpal tunnel symptoms from overgrowth compressing the median nerve, the snoring from macroglossia and obstructive sleep apnea, and the hypertension and new diabetes from growth hormone antagonizing insulin. The bitemporal hemianopsia is the mass, not the hormone — the adenoma compresses decussating nasal retinal fibers at the optic chiasm. Treatment is transsphenoidal resection first line, with somatostatin analogues (octreotide, lanreotide), pegvisomant, or cabergoline for residual disease. Untreated acromegaly roughly doubles mortality through cardiomyopathy, hypertension, and diabetes, and it raises colorectal cancer risk, so these patients need colonoscopy screening.
Sorting the distractors: a random serum growth hormone level is the trap and is specifically not recommended, for the pulsatility reason above; the oral glucose tolerance test with growth hormone measurement is the correct confirmatory test but is the wrong first move — it is more burdensome and is reserved for an elevated or equivocal IGF-1; MRI of the pituitary comes only after biochemistry confirms the diagnosis, and ordering it first inverts the workup; and a 24-hour urinary free cortisol screens for Cushing syndrome — also a pituitary adenoma in Cushing disease, but the wrong hormonal axis entirely, producing central obesity, moon facies, and purple striae rather than acral enlargement.
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