Saliva
Salivary cortisol - General Information
Cortisol is a lipophilic steroid with low molecular weight (MW ~362 Dalton). Following ACTH binding to membrane receptors on cells of the adrenal cortex, cortisol is synthesized and released into the blood stream. Up to 95% of the secreted cortisol will be bound to large proteins (CBG, albumin) and carried throughout the body in the blood. Since the vast majority of cortisol actions rely on binding to its cytosolic mineralocorticoid and glucocorticoid receptors, only the small fraction of unbound, i.e., free cortisol is thought to be biologically active. Due to its low molecular weight and lipophilic nature, unbound cortisol enters cells by passive diffusion which makes it feasible to measure the free cortisol fraction in all bodily fluids. While the assessment of cortisol in sweat or tears is only of theoretical importance and urinary cortisol of decreasing interest, salivary cortisol has become an invaluable tool for both basic scientists and clinicans. A number of significant advantages over the assessment of cortisol in blood has resulted in a steadily increasing interest in salivary cortisol.
FAQs (frequently asked questions) about salivary cortisol
Yes, when compared to the amount of unbound cortisol in serum or plasma samples. A number of studies have revealed correlations between the two specimen of r > 0.90. However, the correlation between the total cortisol levels in blood and salivary cortisol is usually weaker due to different amounts of CBG found in blood (e.g., high levels of CBG due to oral contraceptive use results in high total cortisol levels; free cortisol levels are usually unaltered in states of increased CBG).
A: The easiest way for sampling saliva is to use a device called the "Salivette". The Salivette is manufactured and sold by Sarstedt (http://www.sarstedt.com). Subjects should be instructed to gently chew on the cotton roll to stimulate saliva flow rate. With this it usually takes less than a minute to obtain a saliva sample of 0.5-1 ml volume.
Important:
DO NOT USE THE CITRIC ACID STIMULATED SALIVETTES (green caps)!! Saliva samples obtained with these devices have a low pH which interfers with most immunoassays known. It produces false high cortisol levels. We recommend to use the Salivettes with the blue caps.
No. Studies looking at salivary cortisol levels obtained under minimal and maximal flow rate clearly showed that the cortisol levels in saliva do not depend on flow rate.
We recommend to use dry ice or to send the samples with cooling packs in a polystyrene box. This will prevent the samples from molding. If this is not possible, express shipping is a good alternative.
There are different options available today. First, several diagnostic companies now offer commercial assay kits for cortisol determination in saliva. Three reliable assays are sold by
- IBL (www.ibl-hamburg.com),
- Salimetrics (www.salimetrics.com) and
- Orion (www.diagnostica.orion.fi).
These assays appear to give correct values with acceptable sample volumes required. If you do not have a lab or the time to run the assays yourself, you can also send your samples to a lab which provides assay service. Besides our own lab in Dresden, there are other research labs as well as commercial labs which offer custom assays.
All laboratories should comply with the principles of good laboratory practice (GLP) especially regarding quality assurance. This involves the use of internal and external controls, duplicate or multiple determinations and evaluation of intra- and inter-assay coefficients of variation (CVs) for all analysis.
If you decide to purchase a kit and do the assays in your own lab, the price differs widely and depends on the conditions you obtain from the manufacturer. As a rule of thumb, expect to pay 3-5 USD per duplicate analysis (including standards and controls) for the reagents. If you send your samples to a lab which offers assays service, expect to pay between 2.50 - 15 USD for the same analysis.
Instructions on labelling and shipping samples
Instructions on labelling and shipping saliva samples
Order Form Saliva
(More detailed technical information can be obtained from our scientific papers under "Publications"