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Is the plasma ACTH concentration a reliable parameter in the insulin tolerance test?
1Division of Endocrinology, Department of Medicine 2, University Hospital of Freiburg, Germany. borm@med1.ukl-freiburg.de
European Journal of Endocrinology
|December 4, 2003
Summary
Measuring adrenocorticotropic hormone (ACTH) during an insulin tolerance test (ITT) does not improve evaluation of the hypothalamic-pituitary-adrenal (HPA) axis. Peak ACTH levels show high variability and are not a reliable indicator of HPA axis function.
Area of Science:
- Endocrinology
- Clinical Chemistry
Background:
- The insulin tolerance test (ITT) is a standard method for assessing hypothalamic-pituitary-adrenal (HPA) axis function.
- A peak cortisol level >18 microg/dl typically indicates a sufficient response, but ACTH response standardization is lacking.
Purpose of the Study:
- To evaluate the utility of peak plasma ACTH concentrations in assessing the HPA axis during the ITT.
- To determine if ACTH measurements provide additional diagnostic benefit beyond cortisol levels.
Main Methods:
- Retrospective analysis of 140 ITTs in 125 patients with suspected pituitary insufficiency.
- Prospective evaluation in 15 healthy subjects.
- Analysis of peak plasma ACTH and cortisol concentrations.
Main Results:
- A weak but significant positive correlation was observed between peak ACTH and peak cortisol (rho=0.446, P<0.001), with considerable value spread.
- No specific cut-off ACTH value demonstrated sufficient sensitivity and specificity for identifying HPA axis impairment.
- A peak ACTH <20 pg/ml showed 98% specificity but only 25% sensitivity for secondary adrenal insufficiency (SAI).
Conclusions:
- Peak ACTH concentration is a poor parameter for HPA axis evaluation due to high variability.
- Measuring ACTH during ITT offers no additional benefit compared to cortisol measurements for assessing HPA axis function.