High and low dose clonidine tests for the diagnosis of growth hormone deficiency.

The growth hormone (GH) response to three provocative stimuli was assessed in 15 short normal children (ISS) and 5 children with GH deficiency (GHD). The pharmacologic agents used were insulin 0.1 unit/kg IV (IHT), oral clonidine 0.15 mg/m2 (HDCT) and 25 micrograms irrespective of age and weight (LDCT). Blood glucose and GH were measured at 0, 30, 60, 75, 90 and 120 minutes; and BP and serum cortisol levels were measured during clonidine tests. A steep rise in GH levels were found between 60 and 90 minutes during HDCT and LDCT. The peak GH levels were 29.5 +/- 5.7 ng/ml in HDCT compared to 17.9 +/- 5.7 ng/ml during IHT and 6.7 +/- 2.9 ng/ml during LDCT (p < 0.01). The peak GH levels above 7 ng/ml were seen in 60% children with ISS during LDCT. No significant adverse effects were noticed during HDCT and LDCT except transient drowsiness. The peak GH levels were not related to the fall in BP or cortisol levels. LDCT appears to be a reasonably effective stimulator of GH release. It can be used for screening children with reduced growth velocity as an outpatient procedure. Those with an abnormal response will need a more definite testing such as HDCT.