A 30-year-old athlete's serum GH level is measured at 8 AM after an overnight fast and is found to be undetectable (<0.05 ng/mL). Her IGF-1 is within the normal range. What is the correct interpretation?
- A GH deficiency confirmed; random undetectable GH with normal IGF-1 excludes GH excess
- B Normal finding; GH is secreted in pulses and may be undetectable between pulses in healthy subjects ✓
- C Requires immediate insulin tolerance test to confirm pituitary function
- D Suggests secondary GH deficiency; IGF-1 should also be low in true deficiency
Explanation
GH is secreted in discrete ultradian pulses, primarily during slow-wave sleep, with very low or undetectable trough levels between pulses in normal individuals. A random fasting GH value of zero does not indicate GH deficiency. GH deficiency is confirmed by stimulation tests (insulin tolerance test, glucagon stimulation), where GH fails to rise above 3 ng/mL. Normal IGF-1 further supports adequate integrated GH secretion. Option D is partially true that IGF-1 is low in GH deficiency, but the question scenario shows normal IGF-1, making GH deficiency unlikely; the scenario needs no further emergency testing.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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