Combined simultaneous arginine clonidine stimulation test: Timing of peak growth hormone (GH) concentration and correlation with clinical indices of GH status

Background: The aims of this study were to determine if it is possible to truncate a combined simultaneous arginine clonidine stimulation test, and to correlate the outcome of the test with clinical indices of GH status. Methods: Charts of subjects who underwent a combined simultaneous arginine clonidine stimulation test between January 1, 2007 and August 31, 2016 were reviewed. Results: 131/203 (64.5%) tests performed in children with growth failure demonstrated a peak GH >= 10 ng/ml. 6/7 (85.7%) tests performed in adolescents at the end of GH treatment had a peak GH >= 5 ng/ml. Among these negative tests, 97.8% had a passing GH by 120 min. 58/98 (59.1%) tests that had a sample at 150 min were negative. 3/58 (5.2%) had a passing GH level only at 150 min. Therefore, if the test were shortened to 120 min, 5.2% of normal responders would be missed. There was a weak correlation of peak GH with baseline growth velocity and serum IGF-1 z-score. A trend towards an inverse correlation between peak GH level and change in growth velocity pre- and post-GH was seen. Conclusions: If the combined simultaneous arginine clonidine test were shortened to 120 min, 5.2% of normal responders would be missed. Although this test has not been compared to any "gold standard" GH stimulation test, the outcome of this test does correlate weakly with clinical indices of GH status and spares patients the inconvenience of sequential testing.