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Difficulty: EasyOrdering Laboratory Tests

An occupational health physician evaluates a 48-year-old male construction worker for standard job clearance. The patient mentions that over the past two years, he has had to resize his wedding band twice and purchase larger work boots. He also reports increased daytime somnolence and frequent, dull headaches. Physical examination is notable for a prominent jawline, enlarged hands with thick fingers, and widening spaces between his lower teeth. Vital signs show a blood pressure of 142/90 mm Hg and a heart rate of 76/min. Which of the following is the most appropriate next step in laboratory evaluation?

  1. Serum insulin-like growth factor 1 levelAnswer
  2. B
    Random serum growth hormone level
  3. C
    Oral glucose tolerance test with growth hormone measurement
  4. D
    Magnetic resonance imaging of the pituitary gland
  5. E
    Serum thyroid-stimulating hormone level

Answer

The most appropriate initial laboratory test is a serum insulin-like growth factor 1 level.
The correct answer is the measurement of a serum insulin-like growth factor 1 (IGF-1) level. This patient presents with classic features of acromegaly, including enlargement of the hands and feet (needing larger rings and boots), coarsening of facial features (prominent jaw, spacing of teeth), and sleep apnea (daytime somnolence). Acromegaly is most commonly caused by a growth hormone (GH) secreting pituitary adenoma. Because GH is secreted in a highly pulsatile fashion and has a short half-life, random GH levels are unreliable. IGF-1, which is produced by the liver in response to GH, has a much longer half-life and provides a stable, integrated measure of GH activity over time, making it the most appropriate initial screening laboratory test.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient exhibits classic signs of acral overgrowth (enlarged hands, jaw prominence, widening teeth) and associated symptoms (somnolence, hypertension) highly suspicious for acromegaly.
Recognizing the clinical syndrome dictates the appropriate diagnostic diagnostic pathway.
2
Determine the diagnostic algorithm for the suspected condition.
Diagnosis of acromegaly requires biochemical screening, followed by biochemical confirmation, and finally structural imaging.
Following the correct sequence avoids false positives and unnecessary expensive testing.
3
Select the optimal initial laboratory test.
Serum insulin-like growth factor 1 (IGF-1) is selected as it provides a stable reflection of average growth hormone levels.
Growth hormone itself is pulsatile, making a random draw unreliable for initial screening.

Key Concept

The initial biochemical screening test for suspected acromegaly is the measurement of serum insulin-like growth factor 1 (IGF-1), due to the pulsatile nature of growth hormone secretion.
Estimated Time:1m 0s
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