ABSTRACT
Background: Clonidine provocative test is used for the diagnosis of growth hormone (GH) deficiency. The duration of the test is not uniform across places where it is performed. Aim: To evaluate the frequency and timing of GH peaks during the clonidine test. To determine the timing with the highest diagnostic yield for GH deficiency. Patients and Methods: Analysis of the GH response during a clonidine test performed to 93 children with low stature, aged 11 +/- 3 years (41 percent women), with mean z scores of -2.3 +/- 0.8 for height and of 0.4 +/- 0.9 for body mass index, that were consecutively studied. A oral dose of 0.15 mg/m2 of clonidine was administered and GH levels were determined by the chemiluminescent enzyme immunoassay method of solid phase at 0, +30, +60, +90 and +120 minutes after. The cut-off point for GH deficiency was set at 7 ng/dL. Results: In ten children GH levels were lower than 7 ng/dL during the test and were considered as having GH deficiency. In 86 percent of the 83 patients without GH deficiency, the peak over 7 ng/mL appeared at +60 minutes and in 89 percent the peak had appeared at +90 minutes. In only 11 percent of these children, the peak appeared at +120 minutes. Conclusions: The timing with the highest diagnostic yield for GH is +60 minutes after the administration of clonidine. However the sample at +120 minutes should not be eliminated, considering that the highest GH peak appears at that time in 11 percent of children.