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Salimetrics Cortisol Assay
Background: 195 Saliva specimens covering the range of Cortisol Concentrations in Adults were collected by an Independent Laboratory by Salivette and run against the Salimetrics Salivary Assay, 3 competitive commercially available assays, one in-house assay and against LC-MS/MS
The Salimetrics Cortisol Assay was shown to have the lowest cross reactivity for the problem marker Cortisone. Cortisone is abundant in saliva and has a prolonged half life (280% compared to Cortisol) this can result in a significant impact on the Cortisol value. Therefore, assays with cross-reactivity to Cortisone will give false high Cortisol results.
It was reported in this study and a previous one at the same institution that the Salimetrics Assay had a 0.95 and 0.99 correlation with LC-MS/MS
This was the best correlation of the commercially available assay kits. The Salimetrics assay was also found to be the best commercially available with regard to linearity.
Regarding In-House Assays, it should be born in mind that they are not always produced under good manufacturing principles or ISO quality systems. There is therefore no guarantee that an in-house assay will perform the same on any given day when the analysis is performed, unlike a commercial assay where quality systems operate.
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THE SALIMETRICS RESEARCH LIBRARY
Cortisol (hydrocortisone, Compound F) is the major glucocorticoid hormone produced in the adrenal cortex. Cortisol is actively involved in the regulation of calcium absorption, blood pressure maintenance, anti-inflammatory function, gluconeogenesis, gastric acid and pepsin secretion, and immune function. (1,2,3) Cortisol production has a circadian rhythm. (4) Levels peak in the early morning and drop to the lowest concentration at night. (5) Levels rise independently of circadian rhythm in response to stress. (6) Increased cortisol production is associated with Cushing’s syndrome and adrenal tumors, while decreased cortisol production is associated with adrenal insufficiency (e.g., Addison’s disease) and adrenocorticotropic hormone (ACTH) deficiency. (7)
In the blood only 1 to 15% of cortisol is in its unbound or biologically active form. The remaining cortisol is bound to serum proteins. (8) Unbound serum cortisol enters the saliva via intracellular mechanisms, and in saliva the majority of cortisol remains unbound to protein. (9)
Salivary cortisol levels are unaffected by salivary flow rate or salivary enzymes. (10) Studies consistently report high correlations between serum and saliva cortisol, indicating that salivary cortisol levels reliably estimate serum cortisol levels. (11,12,13)
REFERENCES
1.Migeon, C.J., & Lanes, R.L. (1990). Adrenal cortex: hypo- and hyperfunction. In F. Lifshitz (ed.), Pediatric endocrinology, a clinical guide (2nd ed.), (pp. 333-52). New York: Marcel Dekker.
2.Drucker, S., New, M.I. (1987). Disorders of adrenal steroidogenesis. Pediatr Clin North Am, 34(4), 1055-66.
3.Fischbach, F.T. (1992). The manual of laboratory and diagnostic tests, (4th ed.). Philadelphia: J. B. Lippincott.
4.Dorn, L.D., Lucke, J.F., Loucks, T.L., Berga, S.L. (2007). Salivary cortisol reflects serum cortisol: analysis of circadian profiles. Ann Clin Biochem, 44(pt 3), 281-84.
5.Chernow, B., Alexander, H.R., Smallridge, R.C., et al. (1987). Hormonal responses to graded surgical stress. Arch Intern Med, 147(7), 1273-78.
6.Kreiger, D.T. (1975). Rhythms of ACTH and corticosteroid secretion in health and disease and their experimental modification. J Steroid Biochem, 6(5), 758-91.
7.Rothfield, B. (1974). Plasma cortisol. In: B. Rothfield (ed.), Nuclear medicine–in vitro (pp. 120-5). Philadelphia: Lippincott.
8.Robin, P., Predine, J., Milgrom, E. (1977). Assay of unbound cortisol in plasma. J Clin Endocrinol Metab, 46(2), 277-83.
9.Vining, R.F., McGinley, R.A., Symons, R.G. (1983). Hormones in saliva: mode of entry and consequent implications for clinical interpretation. Clin Chem, 29(10), 1752-56.
10. Vining, R.F., McGinley, R.A. (1987). The measurement of hormones in saliva: Possibilities and pitfalls. J Steroid Biochem, 27(1-3), 81-94.
11. Francis, S.J., Walker, R.F., Riad-Fahmy, D., et al. (1987). Assessment of adrenocortical activity in term newborn infants using salivary cortisol determinations. J of Pediatrics, 111, 129-33.
12. Hiramatsu, R. (1981). Direct assay of cortisol in human saliva by solid phase radioimmunoassay and its clinical applications. Clinica Chimica Acta, 117, 239-249.
Vining, R.F., McGinley, R.A., Maksvytis, J.J., Ho, K.Y. (1983). Salivary cortisol: A better measure of adrenal cortical function than serum cortisol. Ann Clin Biochem, 20
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