The Usefulness of the Combined Growth Hormone (GH)-Releasing Hormone and Arginine Stimulation Test in the Diagnosis of Radiation-Induced GH Deficiency Is Dependent on the Post-Irradiation Time Interval

The diagnostic usefulness of the insulin tolerance test (ITT) in patients with radiation-induced GH deficiency (GHD) is well established, whereas that of the combined GHRH plus arginine stimulation test (AST) is unproven. Both tests were undertaken in 49 adult survivors (aged 16–53.7 yr), who were previously irradiated for nonpituitary brain tumors or leukemia, and 33 age-, gender-, and BMI-matched controls. The aims of the study were to examine the impact of the time interval after irradiation on the pattern of GH responsiveness to the two provocative tests and to establish the role of the GHRH + AST in the diagnosis of radiation-induced GHD. The median (range) peak GH responses to either test were significantly lower (P < 0.0001) in the patients [GHRH + AST, 19.9 (range, 2.7–103.5) μg/liter; ITT, 5 (0.2–34.8) μg/liter] than in normals [GHRH + AST, 55 (5.7–173.5) μg/liter; ITT, 23.8 (4.2–80) μg/liter]. In patients and normal controls, the median peak GH response to the GHRH + AST was significantly greate...