Screening tests for growth hormone deficiency: comparing the efficacy of the Clonidine Stimulation Test with the L-Dopa-Propanolol Test

Abstract

Ninety-one children (39 females, 52 males) were tested for growth hormone (GH) deficiency using the clonidine stimulation test. The mean age was 9.751±3.09 years (range: 2.08-17.92 years). 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 and blood pressure was monitored every 30 minutes. Children who failed the test with a peak GH response of less than 15 mIU/L were subjected to a confirmatory test with insulin induced hypoglycaemia (ITT). The specificity and sensitivity of the test and its side effects were analyzed and compared to that of the L-dopa-propanolol test.

Sixty-two children passed while 29 children failed the test. Of those who failed, 10 were diagnosed as having GHD while 19 (23.5%) subsequently had a normal GH response to ITT (low-responders). Twenty-five children (27.5%) had a significant drop in the systolic blood pressure of >20 mmHg but only 4 (4.4%) complained of dizziness. No patient and 3 patients with adequate GH response will be missed if the 30 and 120 mm samples were omitted respectively. The mean peak GH response for the GHD patients and the low-responders were 8.65±4.73 and 9.02±4.17 mIU/L respectively (p>0.05).

The clonidine stimulation test has a specificity of 76.5%, a positive predictive value of 34.5% and a false positive rate of 23.5%. This is much less specific and sensitive when compared to the L-dopa-propanolol test according to our own experience1 (specificity 87.5%, positive predictive value 63.5% and false positive rate 12.5%). The 30 mm sample can be omitted without significant diagnostic implication. 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 L-dopa test the preferable test for screening for growth hormone deficiency.

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