Salivary cortisol measurement in horses: immunoassay or LC-MS/MS? 2020

F J Sauer, and V Gerber, and S Frei, and R M Bruckmaier, and M Groessl
Swiss Institute of Equine Medicine (ISME), Vetsuisse Faculty, Department of Clinical Veterinary Medicine, University of Bern, and Agroscope, Switzerland, Laenggassstrasse 124, 3012 Bern, Switzerland. Electronic address: fay.sauer@web.de.

The aim of the present study was to measure salivary cortisol concentrations of horses before and after hypothalamic-pituitary-adrenal (HPA) axis stimulation by means of liquid chromatography-tandem-mass spectrometry (LC-MS/MS) and an immunoassay (cELISA) for method comparison. Nine clinically healthy horses participated in the study. An ACTH stimulation test was performed. Saliva samples were collected before (T0) and 60 (T60) min after intravenous injection of 1 μg/kg BW synthetic ACTH1-24. LC-MS/MS was assessed for the determination of equine salivary cortisol. The results of these measurements were then compared to the results obtained by a cELISA, which has previously been validated for use in horses. The Pearson correlation coefficient was calculated and showed no correlation at T0 (r = -0.2452; P = 0.5249) and significantly correlated results at T60 (r = 0.8334; P = 0.0053). Bland-Altman-Plots of T60 revealed that immunoassay measurements led to higher outcome values than LC-MS/MS. On average, immunoassay results were 2.3 times higher. Poor agreement between both methods at T0 is potentially a consequence of inaccuracy in the very low measuring range of the immunoassay, and to a smaller extent, structurally similar cross-reacting agents and matrix effects, which might bias the results. Overestimation of immunoassay results at T60 might be due to different standardization of both methods, non-avoidable matrix effects on the antigen-antibody interaction in the ELISA, and possibly cross-reactions of other steroids. While immunoassay measurements of equine salivary cortisol yielded higher but reasonably correlated results for elevated cortisol concentrations after stimulation of the HPA axis, LC-MS/MS provided more accurate results, particularly for baseline cortisol concentrations close to the limit of detection of the ELISA.

UI MeSH Term Description Entries
D002853 Chromatography, Liquid Chromatographic techniques in which the mobile phase is a liquid. Liquid Chromatography
D004797 Enzyme-Linked Immunosorbent Assay An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed. ELISA,Assay, Enzyme-Linked Immunosorbent,Assays, Enzyme-Linked Immunosorbent,Enzyme Linked Immunosorbent Assay,Enzyme-Linked Immunosorbent Assays,Immunosorbent Assay, Enzyme-Linked,Immunosorbent Assays, Enzyme-Linked
D006736 Horses Large, hoofed mammals of the family EQUIDAE. Horses are active day and night with most of the day spent seeking and consuming food. Feeding peaks occur in the early morning and late afternoon, and there are several daily periods of rest. Equus caballus,Equus przewalskii,Horse, Domestic,Domestic Horse,Domestic Horses,Horse,Horses, Domestic
D006854 Hydrocortisone The main glucocorticoid secreted by the ADRENAL CORTEX. Its synthetic counterpart is used, either as an injection or topically, in the treatment of inflammation, allergy, collagen diseases, asthma, adrenocortical deficiency, shock, and some neoplastic conditions. Cortef,Cortisol,Pregn-4-ene-3,20-dione, 11,17,21-trihydroxy-, (11beta)-,11-Epicortisol,Cortifair,Cortril,Epicortisol,Hydrocortisone, (11 alpha)-Isomer,Hydrocortisone, (9 beta,10 alpha,11 alpha)-Isomer,11 Epicortisol
D000324 Adrenocorticotropic Hormone An anterior pituitary hormone that stimulates the ADRENAL CORTEX and its production of CORTICOSTEROIDS. ACTH is a 39-amino acid polypeptide of which the N-terminal 24-amino acid segment is identical in all species and contains the adrenocorticotrophic activity. Upon further tissue-specific processing, ACTH can yield ALPHA-MSH and corticotrophin-like intermediate lobe peptide (CLIP). ACTH,Adrenocorticotropin,Corticotropin,1-39 ACTH,ACTH (1-39),Adrenocorticotrophic Hormone,Corticotrophin,Corticotrophin (1-39),Corticotropin (1-39),Hormone, Adrenocorticotrophic,Hormone, Adrenocorticotropic
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D012463 Saliva The clear, viscous fluid secreted by the SALIVARY GLANDS and mucous glands of the mouth. It contains MUCINS, water, organic salts, and ptylin. Salivas
D012680 Sensitivity and Specificity Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed) Specificity,Sensitivity,Specificity and Sensitivity
D053719 Tandem Mass Spectrometry A mass spectrometry technique using two (MS/MS) or more mass analyzers. With two in tandem, the precursor ions are mass-selected by a first mass analyzer, and focused into a collision region where they are then fragmented into product ions which are then characterized by a second mass analyzer. A variety of techniques are used to separate the compounds, ionize them, and introduce them to the first mass analyzer. For example, for in GC-MS/MS, GAS CHROMATOGRAPHY-MASS SPECTROMETRY is involved in separating relatively small compounds by GAS CHROMATOGRAPHY prior to injecting them into an ionization chamber for the mass selection. Mass Spectrometry-Mass Spectrometry,Mass Spectrometry Mass Spectrometry,Mass Spectrometry, Tandem

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