Evaluation of the reproducibility of the GHRH plus GHRP-6 test of growth hormone reserve in adults.
BACKGROUND
The diagnosis of GH deficiency (GHD) is controversial, relying on GH secretion elicited by the provocative tests of GH reserve. However, the performance of most of the tests in use have not been evaluated rigorously. The repeatability of a test is a prerequisite before evaluating its diagnostic capability.


OBJECTIVE
The combined administration of GH-releasing hormone (GHRH) and GH-releasing hexapeptide (GHRP-6) is an efficacious test of GH reserve in adults, and the target of this work was to evaluate its reproducibility.


METHODS
Seventeen healthy subjects were challenged with GHRH plus GHRP-6 (1 micro g/kg i.v.). All subjects underwent four tests on different days separated by at least 2 months. GH peaks were evaluated by several mathematical analyses of reproducibility.


RESULTS
As a group, the subjects showed high reproducibility after the four tests, with GH peaks of 46.0 +/- 5.1; 48.4 +/- 6.4; 50.1 +/- 5.4 and 52.9 +/- 5.8 micro g/l, respectively (1 micro g/l = 3 mU/l). Individually analysed, the reproducibility was good, and the regression analysis showed a correlation between tests 1 and 2 of R = 0.729, P < 0.0009, between tests 1 and 3 of R = 0.710, P < 0.001, and between tests 1 and 4 of R = 0.683, P < 0.002. Under mathematical analysis, the multiple correlation coefficient analysis, analysis of variance (anova) with repeated measurements, repeatability index, the simplest coefficient of variation and the intraclass correlation coefficient (ICC) all unambiguously showed that the GHRH + GHRP-6 test was reproducible. Furthermore, the repeated tests did not alter the biochemical diagnosis of the subjects, with absence of false-positive values.


CONCLUSIONS
The GHRH + GHRP-6 test of GH reserve is reproducible in adult subjects.
Popovic
Vera
V
Institute of Endocrinology, University Clinical Centre, School of Medicine and Complejo Hospitalario de Santiago, Santiago de Compostela University, Spain.
Pekic
Sandra
S
Micic
Dragan
D
Damjanovic
Svetozar
S
Marikovic
Jelena
J
Simic
Mirjana
M
Dieguez
Carlos
C
Casanueva
Felipe F
FF
D000328:Adult; D000704:Analysis of Variance; D005260:Female; D013007:Growth Hormone-Releasing Hormone; D019382:Human Growth Hormone / Q000097:blood / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009842:Oligopeptides; D012044:Regression Analysis; D015203:Reproducibility of Results
D009842:Oligopeptides; D019382:Human Growth Hormone; C041048:growth hormone releasing hexapeptide; D013007:Growth Hormone-Releasing Hormone