Arginine Stimulation Test
Used in a child with definite growth retardation and a subnormal physiological growth hormone (GH) stimulation test (i.e. GH < 15 mU/l or 5.7 ng/ml).
Child should be fasting overnight
If the child's bone age is >10 years, the test should be done after sex steroid hormone priming:
M: 100 mg testosterone i.m. 3 days before testing
F: 100 mcg ethinyloestradiol p.o. each for three days before the test.
- Cannulate child.
- Take blood into a plain tube (red top Vacutainer) for baseline GH measurement (0 mins).
- Infuse 0.5 g/kg L-arginine monohydrochloride (maximum dose 40 g) as a 10% solution in normal saline over 30 minutes.
- Take blood for further GH estimation 30, 60, 90, 120 and 150 mins after start of arginine infusion.
- A normal GH response of >15 mU/l (>5.7 ng/ml) excludes GH deficiency.
- A GH response of 7-15 mU/l may indicate partial GH deficiency and should be investigated by a second formal stimulation test.
- A GH response of <7 mU/l (<2.7 ng/ml) should also generally be confirmed by a second test. However, if there are other compatible clinical and auxiliary findings, the child may be directly considered for GH replacement therapy.
- A child with pubertal growth delay may show a subnormal GH response if the test is performed without sex hormone priming. However, there should be a normal response after priming.
SENSITIVITY AND SPECIFICITY
A child with GH deficiency will not respond to this test.
The percentage of children who are not GH deficient and who show a normal response varies from 45 - 93%. Generally, 20% of normal children fail to respond to a formal test and this is the reason for doing 2 tests before proceeding to GH therapy. For example, 71% of normals will respond to both insulin tolerance and arginine stimulation tests. However, the others will respond to at least one test: 13% to insulin, 16% to arginine.
Raiti et al., Lancet 1183 (1967).