Variability in cortisol assays creates an additional problem with setting criteria for a normal response to ACTH that apply to all centers. Two studies comparing cortisol results obtained with different assays showed a positive bias of radioimmunoassays and immunofluorometric enzyme assays of 10 to 50 percent compared with a reference value obtained using isotope dilution gas chromatography-mass spectrometry. As a result, in one study, depending on the combination of assay and criterion used, between 0 and 100 percent of healthy volunteers would be considered to have a normal response to ACTH. This illustrates the difficulty of interpreting cortisol responses that are close to the cutoff point. (3)
Dexamethasone suppression tests are used to assess the status of the hypothalamic-pituitary-adrenal (HPA) axis and for the differential diagnosis of adrenal hyperfunction. The low-dose dexamethasone suppression tests are used to assess nonsuppressible cortisol production by adrenal incidentalomas and to differentiate patients with Cushing's syndrome of any cause from patients who do not have Cushing's syndrome. The high-dose dexamethasone suppression tests help to distinguish patients with Cushing's disease (Cushing's syndrome caused by pituitary hypersecretion of corticotropin [ACTH]) from most patients with the ectopic ACTH syndrome (Cushing's syndrome caused by nonpituitary ACTH-secreting tumors).
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The clinical pathways are based upon publicly available medical evidence and/or a consensus of medical practitioners at The Children’s Hospital of Philadelphia (“CHOP”) and are current at the time of publication. These clinical pathways are intended to be a guide for practitioners and may need to be adapted for each specific patient based on the practitioner’s professional judgment, consideration of any unique circumstances, the needs of each patient and their family, and/or the availability of various resources at the health care institution where the patient is located.
Accordingly, these clinical pathways are not intended to constitute medical advice or treatment, or to create a doctor-patient relationship between/among The Children’s Hospital of Philadelphia (“CHOP”), its physicians and the individual patients in question. CHOP does not represent or warrant that the clinical pathways are in every respect accurate or complete, or that one or more of them apply to a particular patient or medical condition. CHOP is not responsible for any errors or omissions in the clinical pathways, or for any outcomes a patient might experience where a clinician consulted one or more such pathways in connection with providing care for that patient.