Functional tests of adrenal axis in children with measurement of plasma cortisol by competitive protein binding.

The competitive protein binding assay is the method of choice for estimation of plasma cortisol in children. Resting plasma cortisol levels in children without evidence of endocrine disease and with conditions affecting the hypothalamicpituitary-adrenal axis are reported. These showed wide variation, and stimulation tests are therefore essential for diagnosis. A normal response in the 30-minute tetracosactrin (Synacthen) test is defined as an increment of at least 10 μg/ml, with a final level of at least 25 μg/100 ml. 8 children with Addison's disease showed a minimal or negative response and 7 of 9 with hypopituitarism showed a subnormal response. Similar criteria, an increment of at least 10 μg/100 ml, with a final level of at least 25 μg/100 ml one hour after insulin, define a normal response to the intravenous insulin tolerance test. This test provides good discrimination between normal children and those with hypopituitarism, but negative results must be interpreted with caution.