Discrepant results in the diagnosis of GH deficiency with the insulin-tolerance test and the GHRH plus arginine test in patients with traumatic brain injury.
OBJECTIVE
Patients with traumatic brain injury (TBI) are at moderate risk of GH deficiency (GHD), requiring a diagnostic test with high specificity. The GHRH + arginine (GHRH + ARG) test has been recommended as a reliable alternative to the insulin-tolerance test (ITT) as a standard test with a cutoff level of 9 ng/ml. However, it has recently been questioned for its low specificity in obese subjects, and now BMI-dependent cut-off levels are available. In this study, we compared the ITT and GHRH + ARG test in patients with TBI.


METHODS
A cross-sectional study


METHODS
We performed an ITT and a GHRH + ARG test in 21 patients with TBI (6 women, 15 men; mean age 40.2 +/- 12.1 years; BMI 30.7 +/- 6.2). The number of patients classified discordantly as GH deficient by the ITT and the GHRH + ARG test with both classical and BMI-dependent cut-off levels was assessed.


RESULTS
Using the GHRH + ARG test with the classical cut-off (<or= 9 ng/ml), we identified 12 patients as GH deficient who had a normal GH response to ITT (> 3 ng/ml), and one patient as GH sufficient who had a blunted GH response to ITT (discordance rate 61.9%). All patients discordantly classified as GH deficient by the GHRH + ARG test had a BMI of >or= 28. With the BMI-dependent cut-offs (4.2, 8.0, and 11.5 ng/ml in obese, overweight, and lean subjects respectively), only 3 of the 21 patients were discordantly classified (discordance rate 14.3%).


CONCLUSIONS
Our results discourage the use of a cut-off level of 9 ng/ml for the GHRH + ARG test in obese subjects. The diagnostic reliability of this test is improved with the BMI-dependent cut-offs.
Schneider
H J
HJ
Internal Medicine, Endocrinology and Clinical Chemistry, Max Planck Institute of Psychiatry, Kraepelinstr, 10, D-80804 Munich, Germany. schneider@mpipsykl.mpg.de
Herrmann
B L
BL
Schneider
M
M
Sievers
C
C
Schaaf
L
L
Stalla
G K
GK
D000328:Adult; D001120:Arginine / Q000032:analysis*; D015992:Body Mass Index; D001930:Brain Injuries / Q000097:blood / Q000150:complications*; D003430:Cross-Sectional Studies; D003940:Diagnostic Techniques, Endocrine / Q000706:statistics & numerical data; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000032:analysis*; D019382:Human Growth Hormone / Q000172:deficiency*; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D008875:Middle Aged
D019382:Human Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D001120:Arginine