The efficacy of the Clonidine Stimulation Test

Abstract

Objective To review the efficacy of the clonidine stimulation test as a screening test for growth hormone deficiency (GHD) in children with short stature.

Method This is a retrospective review of 86 short children tested for growth hormone (GH) secretion using the clonidine stimulation test. Clonidine at a dosage of 0.1 mg/m2 was given orally after an overnight fast. Blood samples for GH levels were taken from an indwelling catheter at 30, 60, 90 and 120 minutes after medication. Children were recumbent during the test and blood pressure was monitored every 30 minutes. A peak GH response of less than 15 mIU/L was considered abnormal. These children were then subjected to a confirmatory test with insulin induced hypoglycaemia (ITT). The sensitivity and specificity of the test and its side effects were analysed.

Results Of the 86 children, 37 were females and 49 were males. The mean age was 9.59±2.99 years (range: 2.08-16.50 years). Sixty children passed while 26 children failed the test. Of those who failed, 9 were diagnosed as having GHD by failing two tests while 17 (22.1%) subsequently had normal GH response to ITT (low-responders). Twenty-four children (27.9%) had significant drop in the systolic blood pressure of >20 mmHg but only 4 (4.7%) of them complained of dizziness. 88.3% of the peak GH response occurred at 60 and 90 minutes. No patient and 3 patients with adequate GH response will be missed if the 30 min and 120 min samples were omitted respectively. The mean peak GH for the GHD patients and the low-responders were 8.05±4.61 mIU/L and 8.89±4.28 mIU/L respectively (p>0.05).

Conclusion The clonidine stimulation test has a specificity of 77.9% and a positive predictive value of 34.6%. The false positive rate is 22.1% which is much higher than the 12.5% obtained for L-dopa-propanolol test according to our own experience.1 The 30 min sample can be omitted without significant effect. The high false positive rate, the significant drop in systolic blood pressure, the close monitoring and the greater number of samples required for the clonidine stimulation test make the Irdopa the preferable test for screening for growth hormone deficiency.

1J Paediatr Child Health 1994;30:328-30.