Oral clonidine provocative test in the diagnosis of growth hormone deficiency in childhood: Should we make the timing uniform?

Introduction: Oral clonidine is one of the most frequent drugs used for the diagnosis of growth hormone deficiency (GHD), but the duration of the test, depending on which European centres use it, is not uniform and can vary from 120 to 150 min or even 180 min. Subjects and Methods: To standardize this test, evaluating the possibility to shorten it to 90 min, we investigated the response of GH to the oral clonidine test in 291 children evaluated for short stature (height <- 2 SD). Of these, 164 were diagnosed as idiopathic short stature(ISS) and 127 as GHD. In these patients, we calculated: (1) the frequency distribution of the GH peaks to clonidine in GHD and in ISS at various times; (2) the percentage of GH peaks to clonidine before and after 90 min in all and in ISS children; (3) the percentage of the first GH value >= 10 ng/ml before 90 min and after 90 min in ISS. Results: GH peak distribution varied between 30 and 180 min, even though the vast majority of peaks occurred between 30 and 60 min. There was no significant difference (p > 0.05) in the peak distribution between ISS and GHD children. The percentages of GH peaks within 90 min were 92.1% in all children and 95.7% in ISS. If considering the first value of GH >= 10 ng/ml this last percentage reaches 96.3%. Conclusion: Our study suggests that the oral clonidine test can be administered for only 90 min without significantly changing its validity. This test should be standardized at 90 min in European protocols just as in those currently used in the USA in order to reduce the discomfort of patients and the cost of this diagnostic procedure. Copyright (c) 2006 S. Karger AG, Basel