Growth hormone stimulation testing with oral clonidine: 90 minutes is the preferred duration for the assessment of growth hormone reserve.

Provocative growth hormone (GH) testing using oral clonidine, a central alpha2-adrenergic agonist, is routinely performed by many pediatric endocrinologists worldwide. However, there is no clear consensus on the appropriate length of time over which serial blood samples for GH should be obtained for diagnosing GH deficiency. Retrospective analysis of data from oral clonidine GH stimulation testing performed at our center on 66 consecutive patients (42 males), aged 2 to 18 years, was performed to evaluate the clinical utility of obtaining GH samples at 0, 60, 90 and 120 min. In 29 of 30 patients, the presence of a normal GH response was demonstrated by the time of the 90 min sample. It is therefore concluded that serial GH sampling to 90 min is the preferred duration when screening for GH deficiency with clonidine.