Comparison between Insulin-Induced Hypoglycemia and Growth Hormone (GH)-Releasing Hormone + Arginine as Provocative Tests for the Diagnosis of GH Deficiency in Adults1

Abstract

There is now wide consensus that, within an appropriate clinical context, GH deficiency (GHD) in adults must be shown biochemically by provocative testing of GH secretion and that appropriate cut-off limits have to be defined for each provocative test. Insulin-induced hypoglycemia (ITT) is indicated as the test of choice, and severe GHD, to be treated with recombinant human GH replacement, is defined by a GH peak response to ITT of less than 3 micrograms/L. GHRH + arginine (GHRH + ARG) is one of the most promising tests in alternative to ITT. In fact, it has been reported as a potent, reproducible, and age-independent test and that it is able to distinguish between GHD and normal adults. The aim of the present study was to compare the GH response to ITT and GHRH + ARG in a large group of hypopituitary adults (n = 40; 29 male and 11 female; age: 36.4 +/- 2.1 yr). The third centile limit of the peak GH response to ITT has been reported as 5 micrograms/L, whereas in our lab, that to GHRH + ARG is 16.5 micrograms/L. In hypopituitary adults, the mean peak GH response to ITT (1.5 +/- 0.2 micrograms/L, range: 0.1-8.5 micrograms/L) was lower (P < 0.001) than that to GHRH + ARG (3.0 +/- 0.4 micrograms/L, range 0.1-12.0 micrograms/L), though there was positive correlation (r = 0.61, P < 0.001) between the GH responses to the 2 tests. The peak GH response to GHRH + ARG, but not that to ITT, was positively (though weakly) associated with insulin-like growth factor-I levels (r = 0.35, P <…