SFEBES2009 Poster Presentations Steroids (37 abstracts)
Metyrapone interference in serum cortisol immunoassay
David Halsall 1 , Laura Owen 3 , Adam Viljoen 4 , Kevin Taylor 1 , Helen Simpson 1 , Krishna Chatterjee 2 & Mark Gurnell 2
1Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK; 2University of Cambridge Metabolic Research Laboratories, Cambridge, UK; 3University Hospital of South Manchester NHS Foundation Trust, Manchester, UK; 4East and North Hertfordshire NHS Trust, Stevenage, UK.
Metyrapone (MT) is used in the medical management of Cushing’s syndrome as it decreases serum cortisol (CT) levels by inhibiting adrenal β-hydroxylation of 11-deoxycortisol, the final step in CT synthesis. CT precursors, in particular 11-deoxycortisol (DOC), increase following MT therapy. Monitoring glucocorticoid replacement in patients taking MT could therefore be confounded as DOC cross-reacts in commonly used immunoassays (IA) for serum CT. Serum CT results from two patients taking MT and hydrocortisone replacement are presented (Table 1). In both patients, insufficient glucocorticoid replacement was suspected on clinical criteria. In each case serum CT was measured by three commonly used IA; all showed positive bias compared to a liquid chromatography tandem mass spectrometric method (LCMSMS). 11-DOC, the CT precursor, was elevated in both cases.
| Patient | A | B | Cross reactivity |
| Metyrapone dose | 1 g qds | 1 g qds | |
| Hydrocortisone dose | 1.5 mg/h iv | 5 mg tds | |
| ACTH (ng/l) | 68 | 2166 | |
| CT (nmol/l) LCMSMS | 86 | 32 | |
| IA Siemens centaur | 272 | 263 | 0.151* (DOC) |
| IA Beckman | 195 | 204 | 0.181* (DOC) |
| IA Roche | 173 | 169 | 0.035* (DOC) |
| 11-DOC (nmol/l) LCMSMS | 235 | 700 |
Cross reactivity of DOC in each immunoassay was determined by spiking cortisol-free serum with DOC. The observed discrepancy between CT levels measured by IA versus LCMSMS could not be explained by the degree of 11DOC cross reactivity in any of the CT IAs. However the observed positive bias of IAs was proportional to serum (DOC) and (ACTH) levels. This suggests that another ACTH-regulated steroid precursor might cross-react in CT IAs, contributing to their positive bias. Immunoassay methods cannot be relied upon to provide reliable estimates of serum CT in MT treated patients. The precise basis for the positive bias of IAs remains to be elucidated.
Volume 21
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Endocrine Abstracts
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