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

Abstract

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 than normal. Significant correlations were found between both IGF and GH levels and the clinical activity of the disease, the sum of the blood glucose concentrations during the oral glucose tolerance test in non-obese patients, and plasma volume in the patients with normal adrenal and thyroid function. Although significant correlations were found between IGF and GH levels at both time zero (r=0.59) and 60 min (r=0.68) the oral glucose tolerance test, analysis of individual cases indicated that there were differences between the two biological parameters. At 60 min, GH levels above 10 ng/ml were always accompanied by high baseline IGF levels, but half of the cases with GH levels of 5 ng/ml or less also had high IGF values. A quarter of the untreated patients had GH levels of 10 ng/ml or less. Nearly all of the patients with elevated IGF levels had clinical signs of disease activity. These results suggest that measurements of serum somatomedin/IGF levels can be helpful in the diagnosis and assessment the activity of acromegaly.