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Method‐specific serum cortisol responses to the adrenocorticotrophin test: comparison of gas chromatography‐mass spectrometry and five automated immunoassays
Author(s) -
ElFarhan Nadia,
Pickett Alan,
Ducroq David,
Bailey Catherine,
Mitchem Kelly,
Morgan Nicola,
Armston Annie,
Jones Laila,
Evans Carol,
Rees D. Aled
Publication year - 2013
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/cen.12039
Subject(s) - endocrinology , medicine , adrenocorticotropic hormone , chemistry , gas chromatography–mass spectrometry , percentile , immunoassay , chromatography , mass spectrometry , hormone , antibody , immunology , statistics , mathematics
Summary Objective The serum cortisol response to the adrenocorticotrophin ( ACTH ) test is known to vary significantly by assay, but lower reference limits ( LRL ) for this response have not been established by the reference gas chromatography‐mass spectrometry ( GC ‐ MS ) method or modern immunoassays. We aimed to compare the normal cortisol response to ACTH stimulation using GC ‐ MS with five widely used immunoassays. Design, Patients and Measurements An ACTH test (250 μg iv ACTH 1–24 ) was undertaken in 165 healthy volunteers (age, 20–66 years; 105 women, 24 of whom were taking an oestrogen‐containing oral contraceptive pill [ OCP ]). Serum cortisol was measured using GC ‐ MS , A dvia C entaur ( S iemens), A rchitect ( A bbott), M odular A nalytics E 170 ( R oche), I mmulite 2000 ( S iemens) and A ccess ( B eckman) automated immunoassays. The estimated LRL for the 30 min cortisol response to ACTH was derived from the 2·5th percentile of log‐transformed concentrations. Results The GC ‐ MS ‐measured cortisol response was normally distributed in males but not females, with no significant gender difference in baseline or post‐ ACTH cortisol concentration. Immunoassays were positively biased relative to GC ‐ MS , except in samples from women on the OCP , who showed a consistent negative bias. The LRL for cortisol was method‐specific [ GC ‐ MS : 420 n m ; A rchitect: 430 n m ; C entaur: 446 n m ; A ccess 459 n m ; I mmulite (2000) 474 n m ] and, for the E 170, also gender‐specific (female: 524 n m ; male 574 n m ). A separate LRL is necessary for women on the OCP . Conclusions Normal cortisol responses to the ACTH test are influenced significantly by assay and oestrogen treatment. We recommend the use of separate reference limits in premenopausal women on the OCP and warn users that cortisol measurements in this subgroup are subject to assay interference.