Salivary cortisol results obtainable within minutes of sample collection correspond with traditional immunoassays

Abstract

Purpose: Cortisol is frequently assayed as a stress-responsive biomarker which changes over the course of minutes to meet the demands of a person's social context. Salivary cortisol is often used as a noninvasive sampling method that possesses important health implications. A critical barrier to psychobiological research that involves salivary cortisol is a time delay of days to months before cortisol results are obtained via immunoassay, long after the person is no longer proximate to the social context in which they provided the sample. The present study was designed to address this critical barrier through creation of a lateral flow test (LFT) cortisol device capable of measuring salivary cortisol within minutes of sample collection. The LFT is frequently used within commercial point-of-care settings to obtain rapid answers to the presence/absence of a biomarker. The present study extends the LFT into the research domain by presenting performance characteristics of a quantitative LFT that measures salivary cortisol within 20 minutes of sample collection.

Methods: Saliva samples from 29 adults (15 men) were obtained in the morning and afternoon by using Passive Drool and then the Super·SAL Extra Collection Device (hereafter Super·SAL) and later assayed with LFT and a commercially available enzyme immunoassay.

Findings: Results indicate the LFT correlated well with these collection methods (R = 0.872 with Super · SAL, R = 0.739 with Passive Drool, P < 0.0001) and at comparable levels to correspondence of Super · SAL with Passive Drool (R = 0.798, P < 0.0001) which were measured with the same assay.

Implications: These results open an exciting new possibility to integrate this technologic advance into stress research, including knowing and potentially changing the person's social context in a time-sensitive manner. Methodological improvements such as this have the possibility of refining conceptual models of stress reactivity and regulation.

Keywords: collection methods; cortisol; immunoassay; lateral flow technology; stress regulation.

Figure 1

Illustration of the LIAM™ reader and test housing where the VerOFy® LFT strips are integrated, as well as the Super•SAL™ Extra Collection Device.

Figure 2

Timecourse of LFT cortisol suggests the optimal read time is 20 minutes post-collection, but stable reads are achieved earlier.

Figure 3

Example LIAM™ output used to generate T/R Ratio. Like other assays, initial results are reported in optical density and then later converted to concentration values.

Figure 4

Inter-correlations between techniques for measuring cortisol are high. Both Passive Drool and Super•SAL™ cortisol are obtained with a commercially available assay from IBL; LFT cortisol was obtained within 20 minutes of assay start.