Clonidine Stimulation Test For Gh Deficiency: A New Look At Sample Timing

Abstract

In the glucagon stimulation test (GST), the occurrence of peak growth hormone (GH) levels at typical times is an indication of normal secretion. This has not been studied for the clonidine stimulation test (CST). The 120-minute time is rarely the peak, and previous reports suggest it can be omitted. This study aimed to evaluate the meaning and utility of peak time in the CST and the significance of shortening the test. CSTs performed on 250 consecutive subjects in a single center were evaluated for results (GH sufficient or deficient) and result of confirmatory GST with respect to the peak time of the CST. Peak GH occurred typically at 30, 60, and 90 minutes (91.6% of tests, versus 60% expected) (P<.001). A total of 132 of 155 (85.15%) sufficient tests occurred at typical times, versus 66 of 97 (68%) deficient tests (P<.05). Typicality of timing did not follow in the confirmatory GST and did not predict the final result of testing. Removal of the 120-minute sample affected the final result in 0.4% of evaluations. The timing of the GH peak is not useful when interpreting the CST. The CST is equally effective when terminated at 90 minutes from stimulation.