A prospective, randomized, double-blind study compared OCT and PAS activity in 358 patients from 27 different countries [130], by enrolling medically naive acromegaly patients with GH >5 μg/L or GH nadir ≥1 μg/L after an oral glucose tolerance test (OGTT), and IGF-1 above the upper normal limit. Here, IGF1 is linked to acromegaly.