Abstract
Abnormalities in the hypothalamic pituitary adrenal (HPA) axis are identified by a careful analysis of both direct and non-stimulated measurements of the hormones as well as provocative tests. Dynamic testing is useful to determine if elevated levels are suppressible and whether there is sufficient hormone reserve when low levels are measured under stimulation. A combination of all these analyses can distinguish between normal physiology and the consequences of clinical disease in the HPA axis. While clinical suspicion drives the testing performed, arrival at the correct diagnosis by laboratory testing is crucial for cure of the patient. Knowledge of the methodologies used in measuring cortisol and ACTH and associated hormones and binding proteins is essential for correct interpretation of the tests. In this review we compare methodologies available, sensitivity and specificity of the various assays and volumes of sample needed. There are at least 7 different types of dexamethasone suppression testing and they are compared and described in detail. Confirmation of the anatomic source of the hormone is necessary. Petrosal sinus sampling and adrenal vein sampling are reviewed and the clinical indications for each discussed. Finally, once the endocrine diagnosis is reached based on endocrine testing, imaging studies are then reviewed which can confirm the endocrine diagnosis. An abnormality in the HPA axis is a laboratory diagnosis and radiologic imaging is reserved for the last step in the diagnosis of endocrine disease. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.