Radioimmunoassay for the Measurement of Insulin-Like Growth Factor I in Patients with Pituitary Disease in Comparison with Commercially Available Somatomedin-C Radioimmunoassays

A highly sensitive and specific radioimmunoassay for the measurement of insulin-like growth factor I (IGF I) has been developed. The IGF I concentrations were measured in sera of normal subjects, patients with acromegaly, hypophysectomized patients and patients with hyperprolactinaemia. The results were compared with the results obtained after measurement of IGF I in the sera of the same patients with two commercially available radioimmunoassays for somatomedin-C. IGF I was separated from its carrier protein using Sep-Pak C18 cartridges. The total recovery of IGF I by this method was about 100%. The in-house assay shows a high specificity for IGF I and a high sensitivity. As little as 0.1 microgram/l of IGF I can be detected. Only a small amount of serum (25 microliter) is necessary for the IGF I determination and a great number of serum samples (more than 100 per day) can be processed. The mean immunoreactive IGF I concentration was 379 +/- 159 micrograms/l in normal adult subjects, 3340 +/- 1094 micrograms/l in acromegalic patients, and 52 +/- 11 micrograms/l in growth-hormone deficient patients. Patients with hyperprolactinaemia had an IGF I concentration of 433 +/- 112 micrograms/l.