If you suspect that a patient may have acromegaly, what test should you order?
The single best screening test for acromegaly is the plasma level of IGF-1. Unlike GH levels, which are pulsatile and higher at night, samples can be drawn any time of day. In adults, acromegaly is essentially the only condition that causes elevated IGF-1 levels. In children, IGF-1 levels are more difficult to interpret because growing children normally have high levels. IGF-1 levels may be less accurate in mild acromegaly, malnutrition, or hepatic or renal disease.
The patient’s IGF-1 level is not elevated, but you still think that she may have acromegaly. What other test should you order?
The gold standard test to rule out acromegaly is the measurement of serum GH levels in the fasting state and after glucose suppression. Healthy subjects suppress GH levels to < 1 mcg/L 2 hours after an oral glucose load (75 g), whereas patients with acromegaly show insufficient suppression in GH levels. This test may be unreliable in patients with diabetes mellitus, hepatic or renal disease, obesity, pregnancy, or in patients receiving estrogen therapy.