The Importance of Insulin-Like Growth Factor (Somatomedin) Measurements in the Diagnosis and Surveillance of Acromegaly*

Serum somatomedin/insulin-like growth factor (IGF) levels in 92 acromegalic patients were measured, after gel filtration in acetic acid, by means of a competitive proteinbinding assay using specific binding proteins produced by rat liver in culture and human IGF-I as tracer. Results are expressed in comparison with a pool of normal adult serum arbitrarily assigned a value of 1 U/ml. In 37 untreated patients, the mean IGF level was 2.64 ± 0.13 (SEM) U/ml, whereas in 34 normal subjects, it was 1.06 ± 0.03 U/ml. In all patients, IGF levels were above the mean + 2 SD of control values. Among the patients studied after treatment, two thirds of the 43 patients in whom removal of the pituitary tumor was complete had normal or subnormal IGF levels, while the remaining third had values above normal, and 34 patients in whom removal of the pituitary tumor was incomplete had IGF values close to those in untreated patients. In these subjects, cobalt therapy reduced the IGF levels, which, nevertheless, remained higher ...