GH1 and acromegaly: However, reference ranges and clinical thresholds still vary between assays, for example, in Poland, active acromegaly is diagnosed when IGF-1 levels are above 1.0 × ULN and GH suppression is not below 1.0 μg/L using oral glucose tolerance tests (OGTTs) or below 0.4 mg/L using ultrasensitive GH assays (34).