novolytix

Cortisol is the most abundant circulating steroid and the major glucocorticoid secreted by the adrenal cortex. Studies have shown Cortisol is physiologically effective in blood pressure maintenance and anti-inflammatory activity. It is also involved in calcium absorption, gluconeogenesis and the secretion of gastric acid and pepsin.

Most circulating cortisol is bound to cortisol binding protein, transcortin, or albumin. In the absence of cortisol binding proteins in saliva, salivary cortisol is considered to be free and may show a diurnal rhythm with the highest levels in the morning an the lowest levels at night.

Research areas interests include adrenal function, Addisons and Cushings deseases, adrenal hyperplasia, carcinoma, and stress studies.

With our cortisol ELISA kit you can measure in less than two hours the cortisol levels in SALIVA samples. Only a small volume of saliva is needed for the analysis (please check the tables and the IFU for more detailed information).

Readers of this summary may wonder why NovoLytiX has launched an assay for a parameter for which dozens of different ELISA kits are already available in the marketplace.

Background is that we were asked by a research group to conduct a study for which we should measure cortisol among other biomarkers from saliva samples. Hence, we have evaluated five different Cortisol ELISA products from four different manufacturers and were quite shocked about the mediocre comparability of the results we have got with the different kits. Also the absolute values did differ up to factor of 10 between the lowest and highest values for a specific saliva sample. The expected values obtained with 3 of the 5 test kits were (much) higher as compared to published ranges from LC-MS/MS studies. Furthermore, two providers recommend explicitly not to use Salivettes, another provider recommended to use a specific, costly saliva sampling tool, while one manufacturer does not describe the saliva sampling at all. After having experienced and learned all the above, we have decided to develop our own assay with the specific focus i) to produce results as closest as possible to LC-MS/MS and, ii) on the explicit use/recommendation of suitable Salivettes which shall make saliva sampling easy and reproducible.

Important information regarding recommended Salivettes to be used with NovoLytiX’s Direct Saliva ELISA:

• We strongly recommend to use Salivettes with white (transparent) caps containing cotton swabs. These Salivettes can be ordered with NovoLytiX (order code: B-SVC50-U).

• The use of Salivettes with blue caps (e.g. Sarstedt order code: 51.1534.500) containing polystyrene swabs is not recommended although they are specifically designed by Sarstedt for Cortisol determination. They seem to contain constituents which interfere with the ELISA procedure. This is also reported by other Saliva Cortisol ELISA manufacturers. The lower the sample volume collected the more the interference can be observed. Only if the collected saliva volume is higher than 2 mL, the interference is neglectable in NovoLytiX’s Direct Saliva Cortisol ELISA (see also the Direct Saliva Cortisol IFU on pages 3 and 5). 

Summarized here are some key features of our NovoLytiX Direct Saliva Cortisol ELISA:

• Requires 25 µl of saliva per well only.

• All reagents are ready-to-use, except Enzyme Label (Cortisol-HRP conjugate) which presents as ready-to-dilute.

• Two incubation steps only, 60 and 30 minutes at room temperature (18-28°C).

• Standardized against Supelco’s certified Cerilliant® reference Cortisol material (CAS 50-32-7).

• Standard curve range from 0.5 to 50 ng/mL with Limit of Quantitation (LoQ) at 0.35 ng/mL.

• Excellent recovery, accuracy and linearity, all close to 100% over the entire standard range.

• Robust correlation to LC-MS/MS: y = 1.03 x + 0.08 ng/mL, R2 = 0.945 (n =81) see table.